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Pool Evaporation Rate by City: Inches, Gallons and Refill Cost in 25 US Cities

A NOAA-based model of how much water an uncovered 15 x 30 ft residential pool loses to evaporation in 25 US cities, how much normal rainfall gives back, and what refilling costs at utility rates in effect in October 2026.
Pool Evaporation Rate by City: Inches, Gallons and Refill Cost in 25 US Cities
Quick answer

The pool evaporation rate for an uncovered 15 x 30 ft pool ranges from 37.4 inches a year in Nashville to 83.6 inches in Las Vegas across 25 US cities (10,485 to 23,444 gallons), per a NOAA-based model. Refilling costs $26.68 to $368.85 a year at October 2026 rates before rainfall, which replaces most losses in humid cities.

83.6 in
Modelled annual pool evaporation in Las Vegas, NV, highest of 25 US cities (NOAA pan data, 1956 to 1970, x 0.70)
23,444
Gallons a 15 x 30 ft uncovered pool loses to evaporation per year in Las Vegas, NV (modelled)
$368.85
Highest annual cost to replace evaporated water, Houston, TX, before rainfall, rates in effect October 2026 (modelled)
95%
Share of pool evaporation a cover can prevent, upper bound, United States

Five things the model shows

  • Las Vegas, NV has the highest modelled pool evaporation rate of 25 US cities at 83.6 inches a year, based on 1956 to 1970 pan data in NOAA TR NWS 34 and the 0.70 coefficient in NOAA TR NWS 33.
  • Nashville, TN has the lowest at 37.4 inches a year; the highest city loses 2.2 times as much water as the lowest.
  • A 15 x 30 ft pool (an assumption, 450 sq ft) loses a median 13,872 gallons a year to evaporation across the 25 cities, from 10,485 in Nashville to 23,444 in Las Vegas (modelled).
  • Replacing that water costs a median $134.77 a year at rates in effect in October 2026, from $26.68 in Sacramento to $368.85 in Houston, before rainfall (rates via the PC&S cost-to-fill-a-pool rate ledger).
  • Normal 1991 to 2020 rainfall (NOAA NCEI 1991-2020 normals) equals or exceeds modelled evaporation in 8 of 25 cities, and the median cost after rainfall falls to $31.51 a year.
  • In every one of the 25 cities the peak-month pool evaporation rate tops 1 inch a week, from 1.08 inches in San Diego to 2.74 inches in Las Vegas (modelled).
  • A pool cover can prevent up to 95% of evaporation (EPA WaterSense), yet only 15% of pool owners have and regularly use one, per the 2016 Residential End Uses of Water study cited by EPA WaterSense in 2022.
  • The 1956 to 1970 NOAA baseline sits within -4.8% to +0.6% of the Texas Water Development Board 1991 to 2020 averages for five Texas cities.

Pool evaporation rate by city: annual inches and gallons in 25 US cities

Modelled free water surface evaporation for an uncovered pool runs from 37.4 inches a year in Nashville to 83.6 inches in Las Vegas. The desert Southwest sits far above the Southeast, and Texas and Florida cities cluster near 50 inches.

An uncovered residential pool loses water to evaporation every day of the year, not only in swim season.
An uncovered residential pool loses water to evaporation every day of the year, not only in swim season.

This report starts from the monthly Class A pan evaporation means in NOAA TR NWS 34 (Farnsworth and Thompson, 1982). For 24 cities the values are Table II estimates computed from airport weather records for 1956 to 1970 with a form of the Penman equation; for Riverside, CA they are observed pan readings for 1925 to 1978 (Table I). A Class A pan runs warmer than a pool or lake, so NOAA TR NWS 33 converts pan evaporation to free water surface (FWS) evaporation with a coefficient: “The pan coefficient commonly used … is 0.7.”

Las Vegas, NV leads at 83.6 inches a year, followed by Tucson, AZ at 78.0 inches and Phoenix, AZ at 74.8 inches (modelled). Nashville, TN is lowest at 37.4 inches, and Raleigh, NC is next at 37.8 inches. Over a 15 x 30 ft surface, every inch of evaporation equals 280.5 gallons, using 7.48 gallons per cubic foot (Town of Flower Mound).

Annual pool evaporation rate and gallons lost, 15 x 30 ft uncovered pool, 25 US cities (modelled from NOAA 1956 to 1970 pan data)
CityNOAA TR 34 stationPan data periodClass A pan evaporation (in/yr)Pool evaporation, FWS x 0.70 (in/yr)Low, x 0.64 (in/yr)High, x 0.88 (in/yr)Gallons per year, 15 x 30 ft poolPeak monthPeak-month in/weekPeak-month gallons/dayYear-round average in/week
Las Vegas, NVLas Vegas WB Airport1956-1970119.4083.676.4105.123444Jul2.741101.60
Tucson, AZTucson WB Airport1956-1970111.4578.071.398.121883Jun2.481001.50
Phoenix, AZPhoenix WB Airport1956-1970106.8974.868.494.120988Jun2.42971.43
Albuquerque, NMAlbuquerque WB Airport1956-197089.0862.457.078.417491Jun2.20881.20
Dallas, TXDallas WSO1956-197076.7753.749.167.615074Jul1.79721.03
San Antonio, TXSan Antonio WSO1956-197076.5153.649.067.315023Jul1.73691.03
Fort Worth, TXFort Worth WSO1956-197075.9053.148.666.814903Jul1.79721.02
Miami-Dade County (Miami), FLMiami WSO1956-197074.9552.548.066.014716Jul1.27511.01
Fresno, CAFresno WB Airport1956-197074.1751.947.565.314563Jul1.96781.00
Orlando, FLOrlando WB Airport1956-197073.1551.246.864.414363May1.35540.98
Austin, TXAustin WB Airport1956-197073.0051.146.764.214334Jul1.68670.98
Tampa, FLTampa WSO1956-197072.5950.846.563.914253May1.40560.97
Salt Lake City, UTSalt Lake City WB Airport1956-197070.6549.545.262.213872Jul2.11850.95
Sacramento, CASacramento WB Airport1956-197069.6848.844.661.313682Jul1.79720.94
Riverside, CARiverside Citrus Exp1925-1978 (observed Class A pan)69.3848.644.461.113623Jul1.56630.93
Oklahoma City, OKOklahoma City WSFO1956-197067.8247.543.459.713316Jul1.59640.91
Houston, TXHouston WB City1956-197067.7247.443.359.613297Jul1.37550.91
Denver, CODenver WSFO1956-197065.6646.042.057.812892Jul1.55620.88
Los Angeles, CALos Angeles WB Airport1956-197065.0145.541.657.212765Jul1.24500.87
San Diego, CASan Diego WB Airport1956-197060.5442.438.753.311887Jul1.08430.81
Charlotte, NCCharlotte WSO1956-197058.0840.737.251.111404Jul1.21480.78
New Orleans, LANew Orleans WB Moisant1956-197057.9740.637.151.011382Jun1.13450.78
Atlanta, GAAtlanta WB Airport1956-197057.3240.136.750.411255Jun1.16460.77
Raleigh, NCRaleigh Durham WB Airport1956-197054.0237.834.647.510607Jul1.09440.73
Nashville, TNNashville WB Airport1956-197053.4037.434.247.010485Jul1.19480.72

Source: PC&S model from NOAA TR NWS 34 pan means x 0.70 (NOAA TR NWS 33); low and high use the 0.64 and 0.88 coefficients in NOAA TR NWS 33. Download CSV

Annual pool evaporation rate by city, 25 US cities (modelled, inches per year)Point: pan x 0.70. Bar: pan x 0.64 to pan x 0.88 (NOAA range of coefficients)
Annual pool evaporation rate by city, 25 US cities (modelled, inches per year)Range chart of modelled annual free water surface evaporation for 25 US cities. Las Vegas is highest at 83.6 inches a year, followed by Tucson at 78.0 and Phoenix at 74.8. Nashville is lowest at 37.4 inches, with Raleigh, Atlanta, New Orleans and Charlotte near 38 to 41 inches. Bars show the spread from the 0.64 to 0.88 pan coefficients.0306090120Las Vegas, NV: 76.4 to 105, point 83.6Las Vegas, NVTucson, AZ: 71.3 to 98.1, point 78Tucson, AZPhoenix, AZ: 68.4 to 94.1, point 74.8Phoenix, AZAlbuquerque, NM: 57 to 78.4, point 62.4Albuquerque, NMDallas, TX: 49.1 to 67.6, point 53.7Dallas, TXSan Antonio, TX: 49 to 67.3, point 53.6San Antonio, TXFort Worth, TX: 48.6 to 66.8, point 53.1Fort Worth, TXMiami, FL: 48 to 66, point 52.5Miami, FLFresno, CA: 47.5 to 65.3, point 51.9Fresno, CAOrlando, FL: 46.8 to 64.4, point 51.2Orlando, FLAustin, TX: 46.7 to 64.2, point 51.1Austin, TXTampa, FL: 46.5 to 63.9, point 50.8Tampa, FLSalt Lake City, UT: 45.2 to 62.2, point 49.5Salt Lake City, UTSacramento, CA: 44.6 to 61.3, point 48.8Sacramento, CARiverside, CA: 44.4 to 61.1, point 48.6Riverside, CAOklahoma City, OK: 43.4 to 59.7, point 47.5Oklahoma City, OKHouston, TX: 43.3 to 59.6, point 47.4Houston, TXDenver, CO: 42 to 57.8, point 46Denver, COLos Angeles, CA: 41.6 to 57.2, point 45.5Los Angeles, CASan Diego, CA: 38.7 to 53.3, point 42.4San Diego, CACharlotte, NC: 37.2 to 51.1, point 40.7Charlotte, NCNew Orleans, LA: 37.1 to 51, point 40.6New Orleans, LAAtlanta, GA: 36.7 to 50.4, point 40.1Atlanta, GARaleigh, NC: 34.6 to 47.5, point 37.8Raleigh, NCNashville, TN: 34.2 to 47, point 37.4Nashville, TN

Modelled. Uncovered pool, no heating, no shade or wind shelter.

Source: NOAA TR NWS 34 (1956-1970 pan data) x 0.70 pan coefficient (NOAA TR NWS 33); PC&S model. Download chart data (CSV)

How much water a pool loses per week and per day, by month

Evaporation peaks in June or July in most cities and in May in Orlando and Tampa. In the peak month, all 25 cities exceed 1 inch a week; 5 western cities exceed 2 inches.

Las Vegas, NV loses a modelled 2.74 inches a week in July, about 0.391 inches or 110 gallons a day from a 15 x 30 ft pool. Phoenix, AZ peaks at 2.42 inches a week in June. Houston, TX peaks at 1.37 inches a week in July, about 55 gallons a day. San Diego, CA has the lowest peak at 1.08 inches a week (all modelled from NOAA TR NWS 34).

Averaged over the whole year, the rate falls to 0.72 inches a week in Nashville and 1.6 inches a week in Las Vegas. Miami shows the smallest seasonal swing: 0.68 inches a week in January against 1.27 inches in July (modelled).

Monthly pool evaporation rate, 8 US cities (modelled, inches per month)Free water surface evaporation, pan x 0.70
Monthly pool evaporation rate, 8 US cities (modelled, inches per month)Line chart of monthly evaporation for eight cities. Las Vegas peaks at 12.1 inches in July and Phoenix at 10.4 inches in June. Miami stays between 3.0 and 5.6 inches every month, with little seasonal swing. Denver and Sacramento fall below 1.6 inches in winter months and rise to about 7 to 8 inches in July.03.87.511.215JanFebMarAprMayJunJulAugSepOctNovDecLas Vegas, NV, Jan: 2.6Las Vegas, NV, Feb: 3.2Las Vegas, NV, Mar: 5.5Las Vegas, NV, Apr: 7.5Las Vegas, NV, May: 10.3Las Vegas, NV, Jun: 11.8Las Vegas, NV, Jul: 12.1Las Vegas, NV, Aug: 10.8Las Vegas, NV, Sep: 8.4Las Vegas, NV, Oct: 5.8Las Vegas, NV, Nov: 3.2Las Vegas, NV, Dec: 2.4Las Vegas, NVPhoenix, AZ, Jan: 2.5Phoenix, AZ, Feb: 3.0Phoenix, AZ, Mar: 4.9Phoenix, AZ, Apr: 7.0Phoenix, AZ, May: 9.3Phoenix, AZ, Jun: 10.4Phoenix, AZ, Jul: 10.2Phoenix, AZ, Aug: 8.9Phoenix, AZ, Sep: 7.4Phoenix, AZ, Oct: 5.4Phoenix, AZ, Nov: 3.4Phoenix, AZ, Dec: 2.5Phoenix, AZMiami, FL, Jan: 3Miami, FL, Feb: 3.4Miami, FL, Mar: 4.6Miami, FL, Apr: 5.5Miami, FL, May: 5.5Miami, FL, Jun: 4.9Miami, FL, Jul: 5.6Miami, FL, Aug: 5.4Miami, FL, Sep: 4.2Miami, FL, Oct: 4.0Miami, FL, Nov: 3.4Miami, FL, Dec: 3.0Miami, FLHouston, TX, Jan: 2.0Houston, TX, Feb: 2.4Houston, TX, Mar: 3.5Houston, TX, Apr: 4.1Houston, TX, May: 5.2Houston, TX, Jun: 5.9Houston, TX, Jul: 6.0Houston, TX, Aug: 5.5Houston, TX, Sep: 4.5Houston, TX, Oct: 3.8Houston, TX, Nov: 2.5Houston, TX, Dec: 2.0Houston, TXDenver, CO, Jan: 1.5Denver, CO, Feb: 1.6Denver, CO, Mar: 2.7Denver, CO, Apr: 4.0Denver, CO, May: 5.2Denver, CO, Jun: 6.3Denver, CO, Jul: 6.9Denver, CO, Aug: 6.4Denver, CO, Sep: 4.6Denver, CO, Oct: 3.4Denver, CO, Nov: 1.9Denver, CO, Dec: 1.6Denver, COAtlanta, GA, Jan: 1.5Atlanta, GA, Feb: 1.9Atlanta, GA, Mar: 3Atlanta, GA, Apr: 4.0Atlanta, GA, May: 4.9Atlanta, GA, Jun: 5.0Atlanta, GA, Jul: 5.0Atlanta, GA, Aug: 4.7Atlanta, GA, Sep: 3.6Atlanta, GA, Oct: 2.9Atlanta, GA, Nov: 2.0Atlanta, GA, Dec: 1.6Atlanta, GALos Angeles, CA, Jan: 2.5Los Angeles, CA, Feb: 2.5Los Angeles, CA, Mar: 3.6Los Angeles, CA, Apr: 4.0Los Angeles, CA, May: 4.7Los Angeles, CA, Jun: 4.5Los Angeles, CA, Jul: 5.5Los Angeles, CA, Aug: 5.1Los Angeles, CA, Sep: 4.2Los Angeles, CA, Oct: 3.7Los Angeles, CA, Nov: 2.8Los Angeles, CA, Dec: 2.5Los Angeles, CASacramento, CA, Jan: 0.88Sacramento, CA, Feb: 1.5Sacramento, CA, Mar: 2.6Sacramento, CA, Apr: 4.1Sacramento, CA, May: 5.8Sacramento, CA, Jun: 7.5Sacramento, CA, Jul: 7.9Sacramento, CA, Aug: 7.1Sacramento, CA, Sep: 5.4Sacramento, CA, Oct: 3.5Sacramento, CA, Nov: 1.6Sacramento, CA, Dec: 0.85Sacramento, CA

Modelled.

Source: NOAA TR NWS 34 (1956-1970 pan data) x 0.70 pan coefficient (NOAA TR NWS 33); PC&S model. Download chart data (CSV)

Monthly inches for all 25 cities are in the downloadable file “Monthly pool evaporation in inches, 25 US cities (modelled)” below.

Water level at the skimmer is the usual way owners notice evaporation.
Water level at the skimmer is the usual way owners notice evaporation.

Rainfall offsets: net pool water loss after normal precipitation

Rain that falls on the pool surface replaces part of the evaporated water. On 1991 to 2020 normals, rainfall equals or exceeds annual evaporation in 8 of 25 cities, so the refill need in the humid Southeast is a small fraction of the gross loss.

Monthly normal precipitation from the NOAA NCEI 1991-2020 normals was subtracted from each month’s modelled evaporation, with no credit carried between months. Las Vegas, NV normally gets 4.18 inches of rain a year, so rain offsets 5.0% of its evaporation. Houston, TX normally gets 51.84 inches, which offsets 93.1% on a month-by-month basis. New Orleans, LA rainfall meets or exceeds evaporation in every month (modelled).

Gallons evaporated per year from a 15 x 30 ft pool: replaced by normal rainfall vs topped up from the tap, 25 US citiesGallons per year (modelled)
Gallons evaporated per year from a 15 x 30 ft pool: replaced by normal rainfall vs topped up from the tap, 25 US citiesStacked bar chart. In desert cities such as Las Vegas, Phoenix and Tucson most evaporated water must come from the tap because normal rainfall is 4 to 11 inches a year. In New Orleans, Houston, Atlanta, Raleigh, Nashville, Miami and Charlotte normal rainfall replaces 86 percent or more of evaporation on a monthly basis.Las Vegas, NVLas Vegas, NV, net_after_rain: 22,272Las Vegas, NV, replaced_by_rain: 1,172Tucson, AZTucson, AZ, net_after_rain: 18,907Tucson, AZ, replaced_by_rain: 2,976Phoenix, AZPhoenix, AZ, net_after_rain: 18,963Phoenix, AZ, replaced_by_rain: 2,025Albuquerque, NMAlbuquerque, NM, net_after_rain: 15,011Albuquerque, NM, replaced_by_rain: 2,480Dallas, TXDallas, TX, net_after_rain: 5,315Dallas, TX, replaced_by_rain: 9,759San Antonio, TXSan Antonio, TX, net_after_rain: 5,940San Antonio, TX, replaced_by_rain: 9,083Fort Worth, TXFort Worth, TX, net_after_rain: 5,496Fort Worth, TX, replaced_by_rain: 9,407Miami, FLMiami, FL, net_after_rain: 2,029Miami, FL, replaced_by_rain: 12,687Fresno, CAFresno, CA, net_after_rain: 12,233Fresno, CA, replaced_by_rain: 2,330Orlando, FLOrlando, FL, net_after_rain: 2,567Orlando, FL, replaced_by_rain: 11,796Austin, TXAustin, TX, net_after_rain: 4,980Austin, TX, replaced_by_rain: 9,354Tampa, FLTampa, FL, net_after_rain: 3,161Tampa, FL, replaced_by_rain: 11,092Salt Lake City, UTSalt Lake City, UT, net_after_rain: 9,917Salt Lake City, UT, replaced_by_rain: 3,955Sacramento, CASacramento, CA, net_after_rain: 10,681Sacramento, CA, replaced_by_rain: 3,001Riverside, CARiverside, CA, net_after_rain: 11,123Riverside, CA, replaced_by_rain: 2,500Oklahoma City, OKOklahoma City, OK, net_after_rain: 3,202Oklahoma City, OK, replaced_by_rain: 10,114Houston, TXHouston, TX, net_after_rain: 916Houston, TX, replaced_by_rain: 12,381Denver, CODenver, CO, net_after_rain: 8,831Denver, CO, replaced_by_rain: 4,061Los Angeles, CALos Angeles, CA, net_after_rain: 9,567Los Angeles, CA, replaced_by_rain: 3,198San Diego, CASan Diego, CA, net_after_rain: 9,141San Diego, CA, replaced_by_rain: 2,746Charlotte, NCCharlotte, NC, net_after_rain: 1,598Charlotte, NC, replaced_by_rain: 9,806New Orleans, LANew Orleans, LA, net_after_rain: 0New Orleans, LA, replaced_by_rain: 11,382Atlanta, GAAtlanta, GA, net_after_rain: 734Atlanta, GA, replaced_by_rain: 10,521Raleigh, NCRaleigh, NC, net_after_rain: 713Raleigh, NC, replaced_by_rain: 9,894Nashville, TNNashville, TN, net_after_rain: 808Nashville, TN, replaced_by_rain: 9,677net_after_rainreplaced_by_rain

Assumes all rain on the pool surface stays in the pool.

Source: PC&S model; NOAA TR NWS 34; NOAA NCEI 1991-2020 normals. Download chart data (CSV)

Pool evaporation, normal rainfall and net water loss, 15 x 30 ft pool, 25 US cities (evaporation modelled from 1956 to 1970 pan data; rainfall 1991 to 2020 normals)
CityPool evaporation (in/yr)NOAA normal precipitation 1991-2020 (in/yr)NOAA stationNet loss after rain (in/yr)Gross gallons, 15 x 30 ftNet gallons after rainShare offset by rain (%)
Las Vegas, NV83.64.18LAS VEGAS MCCARRAN AP, NV US79.423444222725.0
Phoenix, AZ74.87.22PHOENIX SKY HARBOR INTL AP, AZ US67.620988189639.6
Tucson, AZ78.010.61TUCSON INTL AP, AZ US67.4218831890713.6
Albuquerque, NM62.48.84ALBUQUERQUE INTL AP, NM US53.5174911501114.2
Fresno, CA51.910.99FRESNO YOSEMITE INTL AP, CA US43.6145631223316.0
Riverside, CA48.69.37RIVERSIDE MUNI AP, CA US39.7136231112318.4
Sacramento, CA48.818.14SACRAMENTO EXECUTIVE AP, CA US38.1136821068121.9
Salt Lake City, UT49.515.52SALT LAKE CITY INTL AP, UT US35.413872991728.5
Los Angeles, CA45.512.23LOS ANGELES INTL AP, CA US34.112765956725.0
San Diego, CA42.49.79SAN DIEGO LINDBERGH FLD, CA US32.611887914123.1
Denver, CO46.014.48DENVER INTL AP, CO US31.512892883131.5
San Antonio, TX53.632.38SAN ANTONIO INTL AP, TX US21.215023594060.5
Fort Worth, TX53.135.34FT WORTH MEACHAM FLD, TX US19.614903549663.1
Dallas, TX53.738.32DALLAS LOVE FLD, TX US18.915074531564.7
Austin, TX51.135.57AUSTIN BERGSTROM AP, TX US17.814334498065.3
Oklahoma City, OK47.536.39OKLAHOMA CITY WILL ROGERS AP, OK US11.413316320276.0
Tampa, FL50.849.48TAMPA INTL AP, FL US11.314253316177.8
Orlando, FL51.251.45ORLANDO INTL AP, FL US9.214363256782.1
Miami-Dade County (Miami), FL52.567.41MIAMI INTL AP, FL US7.214716202986.2
Charlotte, NC40.743.60CHARLOTTE DOUGLAS AP, NC US5.711404159886.0
Houston, TX47.451.84HOUSTON INTERCONT AP, TX US3.31329791693.1
Nashville, TN37.450.51NASHVILLE INTL AP, TN US2.91048580892.3
Atlanta, GA40.150.43ATLANTA HARTSFIELD INTL AP, GA US2.61125573493.5
Raleigh, NC37.846.07RALEIGH DURHAM INTL AP, NC US2.51060771393.3
New Orleans, LA40.663.35NEW ORLEANS INTL AP, LA US0.0113820100.0

Source: PC&S model; precipitation from NOAA NCEI 1991-2020 normals (airport stations). Download CSV

Annual cost to replace evaporated pool water at October 2026 rates

Before rainfall, replacing a year of evaporation costs a median $134.77, from $26.68 in Sacramento to $368.85 in Houston. Sewer billing drives the top of the range: cities that bill sewer on every month’s metered water charge sewer on top-up water too.

Each month’s top-up was priced as the increase in that month’s bill over a 9,000-gallon household month (EPA: the average family uses more than 300 gallons a day, EPA WaterSense), using the water and sewer volume tiers compiled in the PC&S cost-to-fill-a-pool rate ledger. Fixed monthly charges do not change and are excluded. Houston, TX costs $368.85 a year at an effective $27.74 per 1,000 gallons (City of Houston, Houston Public Works). Atlanta, GA costs $328.77 a year at $29.21 per 1,000 gallons (City of Atlanta Department of Watershed Management).

Top-up water carries a sewer charge in 8 of 25 cities, where sewer makes up 42.7% to 73.0% of the modelled cost. The desert cities lose the most water but add no sewer charge on it: Las Vegas, NV costs $100.15 a year for 23,444 gallons (Las Vegas Valley Water District), and Phoenix, AZ costs $179.20 for 20,988 gallons (City of Phoenix Water Services Department). After rainfall, Los Angeles, CA has the highest cost at $187.16 a year, and the median across 25 cities drops to $31.51 (modelled).

Annual cost to replace evaporated pool water, 15 x 30 ft pool, 25 US cities (October 2026 rates)US dollars per year, water and sewer volume charges; before and after normal rainfall
Annual cost to replace evaporated pool water, 15 x 30 ft pool, 25 US cities (October 2026 rates)Horizontal bar chart of annual refill cost for evaporated water. Before rainfall, Houston is highest at 368.85 dollars, then Atlanta at 328.77 and Miami at 255.82; Sacramento is lowest at 26.68 dollars. After rainfall, costs fall below 30 dollars in most humid eastern cities, while Los Angeles, Phoenix, Tucson and San Diego stay above 140 dollars.Houston, TX: $369Houston, TX$369Atlanta, GA: $329Atlanta, GA$329Miami, FL: $256Miami, FL$256Los Angeles, CA: $251Los Angeles, CA$251Nashville, TN: $214Nashville, TN$214Charlotte, NC: $201Charlotte, NC$201New Orleans, LA: $196New Orleans, LA$196San Diego, CA: $189San Diego, CA$189Austin, TX: $182Austin, TX$182Tucson, AZ: $179Tucson, AZ$179Phoenix, AZ: $179Phoenix, AZ$179Raleigh, NC: $154Raleigh, NC$154San Antonio, TX: $135San Antonio, TX$135Orlando, FL: $133Orlando, FL$133Tampa, FL: $101Tampa, FL$101Las Vegas, NV: $100Las Vegas, NV$100Salt Lake City, UT: $97.9Salt Lake City, UT$97.9Oklahoma City, OK: $87.5Oklahoma City, OK$87.5Dallas, TX: $87.0Dallas, TX$87.0Fort Worth, TX: $85.5Fort Worth, TX$85.5Denver, CO: $84.3Denver, CO$84.3Albuquerque, NM: $76.4Albuquerque, NM$76.4Riverside, CA: $40.6Riverside, CA$40.6Fresno, CA: $33.9Fresno, CA$33.9Sacramento, CA: $26.7Sacramento, CA$26.7

Modelled. Fixed monthly charges excluded.

Source: PC&S model; utility rate schedules from the PC&S cost-to-fill-a-pool ledger; NOAA TR NWS 34; NOAA 1991-2020 normals. Download chart data (CSV)

Annual cost to replace evaporated water, 15 x 30 ft pool, 25 US cities, water and sewer volume charges at rates in effect in October 2026 (modelled)
CityWater utilityGallons per year (before rain)Annual cost before rain ($)Net gallons after rainAnnual cost after rain ($)Effective $ per 1,000 galSewer charged on top-upsSewer share of cost (%)Water rates effective
Houston, TXCity of Houston, Houston Public Works (Houston Water)13297368.8591625.4027.74Yes54.82026-04-01
Atlanta, GACity of Atlanta Department of Watershed Management (DWM)11255328.7773421.4329.21Yes71.82024-07-01
Miami-Dade County (Miami), FLMiami-Dade Water and Sewer Department (WASD), retail14716255.82202935.2717.38Yes66.62026-10-01
Los Angeles, CALos Angeles Department of Water and Power (LADWP)12765251.219567187.1619.68No0.02026-07-01
Nashville, TNMetro Water Services (Metropolitan Government of Nashville and Davidson County)10485213.7280816.4720.38Yes50.62026-01-01
Charlotte, NCCharlotte Water (City of Charlotte)11404200.94159828.1517.62Yes52.22026-07-01
New Orleans, LASewerage and Water Board of New Orleans (SWBNO)11382196.1300.0017.23Yes42.72021-01
San Diego, CACity of San Diego Public Utilities Department11887188.949141145.2915.89No0.02026-01-01
Austin, TXAustin Water (City of Austin)14334182.48498058.4712.73No0.02026-10-01
Tucson, AZTucson Water (City of Tucson)21883179.4318907153.378.20No0.02026-07-06
Phoenix, AZCity of Phoenix Water Services Department20988179.2018963162.678.54No0.02025-03-01
Raleigh, NCCity of Raleigh, Raleigh Water (Public Utilities)10607153.6071310.3314.48Yes49.02026-07-01
San Antonio, TXSan Antonio Water System (SAWS)15023134.77594053.298.97No0.02026-01-01
Orlando, FLOrlando Utilities Commission (OUC)14363133.15256723.799.27Yes73.02026-10-01
Tampa, FLCity of Tampa Water Department (City of Tampa Utilities billing)14253101.14316118.927.10No0.02026-10-01
Las Vegas, NVLas Vegas Valley Water District (LVVWD), with Southern Nevada Water Authority (SNWA) charges23444100.152227295.194.27No0.02026-01-01
Salt Lake City, UTSalt Lake City Department of Public Utilities1387297.92991770.007.06No0.02026-07-01
Oklahoma City, OKCity of Oklahoma City Utilities Department1331687.48320219.056.57No0.02025-11 (Nov 2025 column; exact day not stated)
Dallas, TXDallas Water Utilities (City of Dallas)1507487.05531529.245.77No0.02026-10-01
Fort Worth, TXFort Worth Water (City of Fort Worth Water Department)1490385.46549631.515.73No0.02026-01-01
Denver, CODenver Water (Denver Board of Water Commissioners)1289284.32883157.756.54No0.02026-01-01 (base rates); temporary drought charges from May 2026 water use through 2027-04-30
Albuquerque, NMAlbuquerque Bernalillo County Water Utility Authority (ABCWUA)1749176.361501165.824.37No0.02026-07-01
Riverside, CARiverside Public Utilities (City of Riverside)1362340.611112333.162.98No0.02026-07-01
Fresno, CACity of Fresno Department of Public Utilities, Water Division1456333.881223328.462.33No0.02016-07-01 (rate level); listed as Current in the Master Fee Schedule effective 2026-07-01
Sacramento, CACity of Sacramento Department of Utilities1368226.681068120.831.95No0.02019-07-01

Source: PC&S model; rate schedules from each utility via the PC&S cost-to-fill-a-pool rate ledger; evaporation from NOAA TR NWS 34; rainfall from NOAA NCEI 1991-2020 normals. Download CSV

Pool cover savings: water and dollars by city

Federal guidance puts cover savings between 30% of make-up water (archived DOE Energy Saver page) and up to 95% of evaporation (EPA WaterSense). At 50%, a 15 x 30 ft pool would save a median 6,936 gallons and $67.38 a year across 25 cities.

EPA WaterSense reports that solid covers can reduce evaporation by more than 90 percent when in use, solar bubble covers by 50 to 95 percent depending on coverage, and liquid evaporation suppressants by 15 percent. The archived DOE Energy Saver page says a cover reduces make-up water by 30% to 50% and chemical use by 35% to 60%. EPA adds that covers “are only effective at reducing evaporation when they are applied.”

In Houston, TX a 50% cut saves $184.43 a year; in Sacramento, CA it saves $13.34 (scenario, before rainfall). Only 15% of pool owners have and regularly use a cover, per the 2016 Residential End Uses of Water study cited by EPA WaterSense. Chemical savings are covered in the pool chemical prices report.

Water and money saved per year by a pool cover at 30%, 50% and 95% evaporation reduction, 15 x 30 ft pool, 25 US cities (scenario, rates in effect October 2026)
CityGallons evaporated per yearGallons saved at 30% (DOE low)Gallons saved at 50% (DOE high)Gallons saved at 95% (EPA maximum)$ saved at 30%$ saved at 50%$ saved at 95%
Houston, TX132973989664812632110.66184.43350.41
Atlanta, GA11255337656281069298.63164.38312.33
Miami-Dade County (Miami), FL14716441573581398076.75127.91243.03
Los Angeles, CA12765383063821212775.36125.60238.65
Nashville, TN1048531465242996164.12106.86203.03
Charlotte, NC11404342157021083460.28100.47190.90
New Orleans, LA11382341556911081358.8498.07186.32
San Diego, CA11887356659441129356.6894.47179.49
Austin, TX14334430071671361764.6998.34174.07
Tucson, AZ218836565109422078960.4494.44170.93
Phoenix, AZ209886296104941993953.7689.60170.24
Raleigh, NC10607318253041007746.0876.80145.92
San Antonio, TX15023450775121427240.4367.38128.03
Orlando, FL14363430971821364539.9466.57126.49
Tampa, FL14253427671261354037.4360.2797.16
Las Vegas, NV234447033117222227233.4155.0896.00
Salt Lake City, UT13872416269361317829.3848.9693.02
Oklahoma City, OK13316399566581265029.8947.8683.52
Dallas, TX15074452275371432031.7850.4083.42
Fort Worth, TX14903447174521415825.6442.7381.19
Denver, CO12892386864461224725.2942.1680.10
Albuquerque, NM17491524787461661622.9138.1872.55
Riverside, CA13623408768121294212.1820.3138.58
Fresno, CA14563436972821383510.1616.9432.18
Sacramento, CA1368241056841129988.0013.3425.35

Source: PC&S scenario; percentages from archived DOE Energy Saver page and EPA WaterSense; gallons and costs from the PC&S model. Download CSV

How the NOAA-based pool evaporation rate compares with newer and local data

The NOAA pan data are from 1956 to 1970, so the model was checked against four newer or local sources. Most checks agree within about 5%; the largest gaps come from stations that sit away from the city airport.

The Texas Water Development Board publishes monthly gross lake evaporation by one-degree quadrangle through December 2025. Against its 1991 to 2020 means, the model is -3.9% in Houston, -4.8% in Dallas, -4.8% in Fort Worth, -1.5% in Austin and +0.6% in San Antonio. TWDB’s 2016 to 2025 means are lower than its 1991 to 2020 means in all five quadrangles, so recent years do not show a rise that would make the older NOAA baseline too low.

Oklahoma State University Extension estimated 33.7 inches of May to October shallow-water evaporation for central Oklahoma (climate division 5, which contains Oklahoma City per the Oklahoma Climatological Survey) for 1997 to 2013; the model gives 32.9 inches for Oklahoma City (-2.4%). The City of Mesa evaporation chart totals 79 inches a year for the Phoenix area; the model gives 74.8 inches (-5.3%).

Model check: annual pool evaporation rate vs newer or local estimates, 10 US cities (inches)
CityComparison sourceComparison periodComparison value (in)This model (in)Model vs comparison (%)
Phoenix, AZCity of Mesa evaporation chart (400 sq ft pool, Valley average)not stated79.074.8-5.3
Houston, TXTWDB gross lake evaporation, quadrangle 8121991-202049.347.4-3.9
Dallas, TXTWDB gross lake evaporation, quadrangle 5111991-202056.453.7-4.8
Fort Worth, TXTWDB gross lake evaporation, quadrangle 5101991-202055.853.1-4.8
Austin, TXTWDB gross lake evaporation, quadrangle 7101991-202051.951.1-1.5
San Antonio, TXTWDB gross lake evaporation, quadrangle 8091991-202053.353.60.6
Oklahoma City, OK (May to Oct only)OSU Extension, climate division 5 (Central), Mesonet-based1997-201333.732.9-2.4
Tucson, AZWRCC pan record x 0.70, Tucson U of Ariz #11982-200577.778.00.3
Las Vegas, NVWRCC pan record x 0.70, Boulder City1931-200481.283.62.9
Riverside, CAWRCC pan record x 0.70, Riverside Citrus Exp St1948-200553.048.6-8.2
Phoenix, AZWRCC pan record x 0.70, Mesa1896-200566.174.813.2

Sources: Texas Water Development Board; Oklahoma State University Extension; City of Mesa; Western Regional Climate Center pan records converted with 0.70; PC&S model. Download CSV

Evaporation vs swim season length: water loss continues after closing

Cities with longer swim seasons tend to evaporate more water (Spearman 0.64 across 23 metros), but a large share of evaporation happens outside the season. The median city loses 34.5% of its annual evaporation on days when the normal high is below 80F.

Swim-season windows (days with a normal high of 80F or more) come from the PC&S pool season length report, built on NOAA 1991 to 2020 daily normals. Denver, CO has a 102-day season and loses 54.8% of its evaporation outside it; Raleigh, NC loses 50.0%. Phoenix, AZ, with a 232-day season, loses 18.5% outside it (modelled). Los Angeles and San Diego airports log no days at 80F, so all their evaporation falls outside that definition.

Share of annual pool evaporation that happens outside the swim season, 22 US cities (modelled)Percent of annual evaporation on days with a normal high below 80F
Share of annual pool evaporation that happens outside the swim season, 22 US cities (modelled)Horizontal bar chart. Denver loses 54.8 percent of its annual evaporation outside its swim season, Raleigh 50.0 and Charlotte 47.4. Phoenix loses the least outside the season at 18.5 percent, followed by Miami at 20.5 and Tucson at 24.1.Denver, CO: 54.8%Denver, CO54.8%Raleigh, NC: 50%Raleigh, NC50%Charlotte, NC: 47.4%Charlotte, NC47.4%Atlanta, GA: 46.5%Atlanta, GA46.5%Salt Lake City, UT: 46.2%Salt Lake City, UT46.2%Oklahoma City, OK: 46%Oklahoma City, OK46%Nashville, TN: 43.1%Nashville, TN43.1%Riverside, CA: 39.1%Riverside, CA39.1%Dallas, TX: 37.7%Dallas, TX37.7%New Orleans, LA: 37.3%New Orleans, LA37.3%Fort Worth, TX: 36.9%Fort Worth, TX36.9%Houston, TX: 32.1%Houston, TX32.1%Sacramento, CA: 32.1%Sacramento, CA32.1%Fresno, CA: 29.9%Fresno, CA29.9%San Antonio, TX: 29.9%San Antonio, TX29.9%Austin, TX: 29.8%Austin, TX29.8%Las Vegas, NV: 29.3%Las Vegas, NV29.3%Orlando, FL: 27.5%Orlando, FL27.5%Tampa, FL: 27.1%Tampa, FL27.1%Tucson, AZ: 24.1%Tucson, AZ24.1%Miami, FL: 20.5%Miami, FL20.5%Phoenix, AZ: 18.5%Phoenix, AZ18.5%

Los Angeles and San Diego airports have no days at 80F in the season report and are excluded from this chart.

Source: PC&S model; NOAA TR NWS 34; PC&S Pool Season Length by City (NOAA 1991-2020 daily normals). Download chart data (CSV)

Swim-season length and pool evaporation inside and outside the season, 24 US cities (season from NOAA 1991 to 2020 normals; evaporation modelled from 1956 to 1970 pan data)
CityMetro (season report)Swim-season days (normal high >= 80F)Season windowPool evaporation (in/yr)Evaporation inside season (in)Share of evaporation outside season (%)
Los Angeles, CALos Angeles-Long Beach-Anaheim, CA0No days at 80F45.50.0100.0
San Diego, CASan Diego-Chula Vista-Carlsbad, CA0No days at 80F42.40.0100.0
Denver, CODenver-Aurora-Centennial, CO102Jun 6 to Sep 1546.020.854.8
Raleigh, NCRaleigh-Cary, NC131May 17 to Sep 2437.818.950.0
Charlotte, NCCharlotte-Concord-Gastonia, NC-SC133May 16 to Sep 2540.721.447.4
Atlanta, GAAtlanta-Sandy Springs-Roswell, GA142May 11 to Sep 2940.121.546.5
Salt Lake City, UTSalt Lake City-Murray, UT105Jun 5 to Sep 1749.526.646.2
Oklahoma City, OKOklahoma City, OK130May 20 to Sep 2647.525.746.0
Nashville, TNNashville-Davidson-Murfreesboro-Franklin, TN138May 15 to Sep 2937.421.343.1
Riverside, CARiverside-San Bernardino-Ontario, CA164May 18 to Oct 2848.629.639.1
Dallas, TXDallas-Fort Worth-Arlington, TX161May 5 to Oct 1253.733.537.7
New Orleans, LANew Orleans-Metairie, LA179Apr 23 to Oct 1840.625.437.3
Fort Worth, TXDallas-Fort Worth-Arlington, TX161May 5 to Oct 1253.133.536.9
Houston, TXHouston-Pasadena-The Woodlands, TX193Apr 15 to Oct 2447.432.232.1
Sacramento, CASacramento-Roseville-Folsom, CA155May 12 to Oct 1348.833.132.1
Fresno, CAFresno, CA160May 7 to Oct 1351.936.429.9
San Antonio, TXSan Antonio-New Braunfels, TX193Apr 14 to Oct 2353.637.529.9
Austin, TXAustin-Round Rock-San Marcos, TX192Apr 15 to Oct 2351.135.929.8
Las Vegas, NVLas Vegas-Henderson-North Las Vegas, NV180Apr 22 to Oct 1883.659.129.3
Orlando, FLOrlando-Kissimmee-Sanford, FL227Mar 25 to Nov 651.237.127.5
Tampa, FLTampa-St. Petersburg-Clearwater, FL223Apr 1 to Nov 950.837.027.1
Tucson, AZTucson, AZ218Apr 1 to Nov 478.059.224.1
Miami-Dade County (Miami), FLMiami-Fort Lauderdale-West Palm Beach, FL265Mar 8 to Nov 2752.541.720.5
Phoenix, AZPhoenix-Mesa-Chandler, AZ232Mar 22 to Nov 874.861.018.5

Source: PC&S model; season windows from the PC&S pool season length report. Download CSV

Leak or evaporation: official tests and thresholds

EPA WaterSense treats a loss of more than 2 inches a week, or 3 inches in hot, dry areas, as a likely leak. The modelled peak-month rate stays under 2 inches a week in 20 of 25 cities and under 3 inches in all 25.

The bucket test compares the pool's water loss with a bucket of water exposed to the same conditions.
The bucket test compares the pool’s water loss with a bucket of water exposed to the same conditions.
  • EPA WaterSense bucket test: on a day without rain or heavy wind, shut off pool systems and the autofill, set a 2.5 to 5 gallon bucket on a step, mark the bucket and pool levels, and compare after 24 hours. If the pool drops more than the bucket, the pool may have a leak.
  • City of Mesa version: compare after two or three days, then repeat for 24 hours with the pump on and 24 hours with it off; more loss with the pump on points to plumbing.
  • The City of Mesa estimates that up to 30% of all pools may have a leak, and that an autofill valve can hide it.

Model outputs

Annual pool evaporation per city, in inches and gallons

How much water does an uncovered 15 x 30 ft pool lose to evaporation each year in each city?

FormulaAnnual inches = sum of 12 monthly Class A pan means x 0.70; gallons = inches x 450 sq ft / 12 x 7.48

Inputs: Fact rows 1 (0.70 coefficient), 7 (7.48 gal per cubic foot) and the 25 pan_ rows (NOAA TR 34); derived D1, D2

37.4 inches (10,485 gallons) in Nashville to 83.6 inches (23,444 gallons) in Las Vegas; median 49.5 inches and 13,872 gallons.

Limitations: Pan data from 1956 to 1970; one national coefficient; no heating, shade, wind shelter, splash-out or backwash.

Annual refill cost at official utility rates

What does it cost to replace that water at rates in effect in October 2026?

FormulaSum over months of bill(9,000 gal + top-up) minus bill(9,000 gal), water and sewer volume tiers; two-month bills priced in month pairs

Inputs: Derived gallons per city; the 25 rate_ fact rows (utility schedules via the PC&S fill-cost ledger); fact row 10 (EPA 300 gal/day)

$26.68 (Sacramento) to $368.85 (Houston) before rainfall, median $134.77; after rainfall $0.00 (New Orleans) to $187.16 (Los Angeles), median $31.51.

Limitations: Fixed charges excluded; winter-average sewer effects not modelled; rates change, so costs are a snapshot.

Pool cover savings scenario

How much water and money would a pool cover save in each city?

FormulaGallons saved = annual gallons x 30%, 50% or 95%; dollars saved = annual cost minus the cost of the remaining top-ups

Inputs: Fact rows for DOE 30% and 50% (archived) and EPA 95%; derived gallons and costs per city

At 50%, a median 6,936 gallons and $67.38 a year; from $13.34 in Sacramento to $184.43 in Houston.

Limitations: Savings depend on how many hours the cover is on; a solid cover also keeps rain out, which this scenario ignores.

Evaporation vs swim season length

Do cities with longer swim seasons lose more water, and how much is lost outside the season?

FormulaSpearman and Pearson correlation of annual FWS inches vs swim-season days at 80F; out-of-season share = evaporation on days outside the season window / annual

Inputs: Derived FWS per city; season_ fact rows (PC&S season report, NOAA 1991 to 2020 daily normals)

Spearman 0.64 and Pearson 0.45 across 23 metros; out-of-season share from 18.5% (Phoenix) to 54.8% (Denver), median 34.5%.

Limitations: Association only; daily evaporation spread evenly within each month; 80F threshold is one definition of swim season.

Rainfall offset

How much of the evaporated water does normal rainfall replace?

FormulaNet inches = sum over months of max(0, FWS minus normal precipitation); offset = 1 minus net / gross

Inputs: Derived FWS per city; prcp_ fact rows (NOAA NCEI 1991-2020 monthly normals)

From 5.0% in Las Vegas to 100.0% in New Orleans; rainfall equals or exceeds annual evaporation in 8 of 25 cities.

Limitations: Assumes all rain stays in the pool; ignores overflow, draining and dry spells within a month.

Rule-of-thumb check

Does the common quarter-inch-a-day rule match the data?

Formula0.25 inches x 365 days = 91.25 inches a year, compared with modelled annual evaporation

Inputs: Fact rows for the Latham rule of thumb and the Flower Mound estimate; derived FWS and peak-day rates per city

91.25 inches a year exceeds the modelled total for all 25 cities, including Las Vegas at 83.6 inches; a quarter inch a day is reached only in the peak month, and only in 9 of 25 cities. The Town of Flower Mound summer estimate of half an inch a day is about double the modelled July rate for Dallas and Fort Worth (0.255 inches a day).

Limitations: Rule of thumb is not location-specific; heated or windy pools can exceed it.

Download the calculation sheet (CSV)

Results by the numbers

  1. Las Vegas, NV: 83.6 inches of modelled pool evaporation a year, or 23,444 gallons from a 15 x 30 ft pool (NOAA pan data 1956 to 1970, NOAA TR NWS 34).
  2. Tucson, AZ: 78.0 inches a year; Phoenix, AZ: 74.8 inches a year; Albuquerque, NM: 62.4 inches a year (modelled, NOAA TR NWS 34).
  3. Nashville, TN: 37.4 inches a year, the lowest of 25 US cities; Raleigh, NC: 37.8 inches; Atlanta, GA: 40.1 inches (modelled, NOAA TR NWS 34).
  4. The median city in the 25-city set loses 49.5 inches a year to evaporation (modelled, pan x 0.70, NOAA TR NWS 33).
  5. Las Vegas peaks at 2.74 inches a week in July, about 110 gallons a day from a 15 x 30 ft pool (modelled from NOAA TR NWS 34).
  6. 5 of 25 cities exceed 2 inches a week in their peak month: Albuquerque, Las Vegas, Phoenix, Salt Lake City, Tucson (modelled). EPA WaterSense treats loss above 2 inches a week, or 3 inches in hot, dry areas, as a likely leak.
  7. Houston, TX: $368.85 a year to replace evaporated water before rainfall at City of Houston rates effective 2026-04-01, because sewer is billed on each month’s metered water (City of Houston, Houston Public Works).
  8. Sacramento, CA: $26.68 a year, the lowest of 25 cities, at a flat-fee sewer and a single water rate effective 2019-07-01 (City of Sacramento Department of Utilities).
  9. After normal rainfall, Los Angeles, CA has the highest modelled refill cost at $187.16 a year, because LAX normally gets 12.23 inches of rain against 45.5 inches of evaporation (NOAA NCEI 1991-2020 normals).
  10. New Orleans, LA: normal monthly rainfall at the New Orleans International Airport station (63.35 inches a year, 1991 to 2020) meets or exceeds modelled evaporation in every month, so the net refill need is 0 gallons (NOAA NCEI 1991-2020 normals).
  11. A cover that cuts evaporation by 50%, the top of the 30% to 50% make-up water range on the archived DOE Energy Saver page, would save a median $67.38 and 6,936 gallons a year per 15 x 30 ft pool across the 25 cities (scenario).
  12. Denver, CO loses 54.8% of its annual pool evaporation on days outside its 80F swim season; Phoenix, AZ loses 18.5% (modelled with the PC&S pool season length report).
  13. Across 23 metros, annual evaporation and swim-season length are positively associated (Spearman rank correlation 0.64, Pearson 0.45), not perfectly linked (PC&S calculation).
  14. Houston’s Texas Water Development Board quadrangle recorded 52.0 inches of gross lake evaporation in 2025, against a 1991 to 2020 mean of 49.3 inches (Texas Water Development Board, data through December 2025).

FAQ

What is a normal pool evaporation rate?

Across 25 US cities the modelled annual rate runs from 37.4 to 83.6 inches, with a median of 49.5 inches, based on NOAA TR NWS 34 pan data and the 0.70 coefficient in NOAA TR NWS 33.

Which US city has the highest pool evaporation rate?

Las Vegas, NV, at 83.6 inches a year, or 23,444 gallons from a 15 x 30 ft pool (modelled from NOAA TR NWS 34).

Which city in the study has the lowest pool evaporation rate?

Nashville, TN, at 37.4 inches a year, or 10,485 gallons from a 15 x 30 ft pool (modelled from NOAA TR NWS 34).

Does rain make up for pool evaporation?

In 8 of 25 cities, 1991 to 2020 normal rainfall (NOAA NCEI 1991-2020 normals) equals or exceeds annual evaporation. In Las Vegas, rain offsets only 5.0%.

Why is pan evaporation multiplied by 0.70?

A Class A pan gains heat through its sides and bottom and evaporates faster than a pool or lake. NOAA TR NWS 33 gives 0.7 as the commonly used coefficient and a May to October range of 0.64 to 0.88.

How many gallons is one inch of water in a 15 x 30 ft pool?

280.5 gallons, from 450 sq ft x 1/12 ft x 7.48 gallons per cubic foot (Town of Flower Mound).

Is the quarter-inch-a-day rule accurate?

As a year-round average it is too high. A quarter inch a day equals 91.25 inches a year, above the modelled total for every one of 25 cities; Las Vegas tops the list at 83.6 inches (NOAA TR NWS 34).

Does a pool keep evaporating after swim season ends?

Yes. Denver, CO loses 54.8% of its annual evaporation on days with a normal high below 80F; the median across 22 cities with a season is 34.5% (modelled with the PC&S pool season length report).

How much money can a pool cover save on water?

At a 50% cut (archived DOE Energy Saver page), a 15 x 30 ft pool saves a median $67.38 a year across 25 cities, and $184.43 in Houston (scenario at October 2026 rates).

Are 1956 to 1970 evaporation data still valid?

For the cities checked, yes within a few percent: the model sits -4.8% to +0.6% from Texas Water Development Board 1991 to 2020 averages in five Texas cities and -2.4% from an Oklahoma State University Extension 1997 to 2013 estimate for central Oklahoma.

More questions answered

How much water does a pool lose per day?

In the peak month, a 15 x 30 ft uncovered pool loses a modelled 0.391 inches a day (110 gallons) in Las Vegas in July and 0.195 inches (55 gallons) in Houston in July, based on NOAA TR NWS 34 pan data x 0.70. Averaged over the year, Las Vegas loses 0.23 inches a day.

Is it normal for a pool to lose an inch of water a week?

Yes in summer. The modelled peak-month rate exceeds 1 inch a week in all 25 cities, from 1.08 inches in San Diego to 2.74 inches in Las Vegas. EPA WaterSense flags more than 2 inches a week, or 3 inches in hot, dry areas, as a likely leak.

How do I know if my pool is leaking or evaporating?

Run a bucket test: set a bucket of water on a pool step, mark both levels, switch off the autofill and compare after 24 hours (EPA WaterSense) or two to three days (City of Mesa). If the pool drops more than the bucket, a leak is likely.

Does a pool cover stop evaporation?

A cover can prevent up to 95% of evaporation (EPA WaterSense); solid covers cut it by more than 90% when in use and solar covers by 50% to 95% (EPA WaterSense). The archived DOE Energy Saver page puts the reduction in make-up water at 30% to 50%.

How much does it cost to top off a pool?

Replacing a year of evaporation from a 15 x 30 ft pool costs a median $134.77 across 25 US cities at October 2026 rates before rainfall, from $26.68 in Sacramento to $368.85 in Houston (modelled with the PC&S cost-to-fill-a-pool rate ledger).

Assumptions and method

  1. Selected the 25 cities with official water and sewer rate schedules in the PC&S cost-to-fill-a-pool ledger (rates in effect 2026-10-04).
  2. Typed the monthly Class A pan evaporation means for each city’s airport station from NOAA TR NWS 34 Table II (Riverside: Table I) and checked each row against the printed page images.
  3. Converted pan to free water surface evaporation with the 0.70 coefficient from NOAA TR NWS 33 (sensitivity: 0.64 and 0.88).
  4. Converted inches to gallons for an assumed 15 x 30 ft (450 sq ft) pool surface at 7.48 gallons per cubic foot.
  5. Subtracted NOAA NCEI 1991-2020 monthly precipitation normals month by month for the net-of-rain estimate.
  6. Priced each month’s top-up as the increment over a 9,000-gallon household month, using the ledger’s water and sewer volume tiers.
  7. Applied cover savings of 30%, 50% (DOE, archived) and 95% (EPA upper bound) as scenarios.
  8. Checked the model against TWDB 1991-2020 lake evaporation, an OSU Mesonet-based estimate, the City of Mesa chart and WRCC pan records.
  9. Joined swim-season windows from the PC&S season report to compute out-of-season shares and correlations.

Included: Government, academic and utility sources opened on 2026-10-07 (utility schedules compiled 2026-10-04); pan station data with at least 10 years of record per NOAA TR 34 rules.

Excluded: Unsourced evaporation charts, commercial calculators and statistics without a stated method; see excluded.md.

Conflicting numbers: Where sources differ (for example the City of Mesa 79-inch chart vs 74.8 inches modelled for Phoenix), both are shown with the percentage gap. Rules of thumb are compared with the model, not used as inputs.

Derived metrics: All derived values are in derived.csv with formulas and input rows, reproducible with scripts/compute.py, make_facts.py and make_tables.py.

Caveats

  • Pan data cover 1956 to 1970 (Riverside 1925 to 1978); newer data exist only for some cities and were used as checks.
  • One national coefficient (0.70) is applied; NOAA map 4 coefficients vary from 0.64 to 0.88 by location.
  • The 15 x 30 ft pool is an assumption, not a national average; scale gallons and costs by surface area.
  • Heated pools, water features, wind exposure, shade, splash-out, backwash and leaks are not modelled.
  • Net-of-rain figures assume all rain stays in the pool; costs exclude fixed charges and winter-average sewer effects.
  • Airport stations may differ from neighborhood conditions within a metro.

Method last reviewed October 7, 2026.

Data vintage and updates

  • The U.S. Department of Energy Energy Saver page on pool covers returned HTTP 404 when checked on 2026-10-07; this report cites the archived capture of 2025-01-10 for the 30% to 50% make-up water figure (archived DOE Energy Saver page).
  • Water rate schedules effective 2026-10-01 for Austin Water, Dallas Water Utilities, Miami-Dade WASD, OUC (Orlando) and the City of Tampa are used in the refill model (PC&S cost-to-fill-a-pool rate ledger).
  • Schedules effective in July 2026 apply for Albuquerque, Charlotte, Los Angeles (LADWP), Raleigh, Riverside and Salt Lake City (2026-07-01) and Tucson (2026-07-06) (PC&S cost-to-fill-a-pool rate ledger).
  • The Texas Water Development Board updated its quadrangle lake evaporation data through December 2025. San Antonio’s quadrangle 809 recorded 58.6 inches of gross evaporation in 2025, against a 1991 to 2020 mean of 53.3 inches.
  • City of Houston water rates effective 2026-04-01 set the top water tier at $20.20 per 1,000 gallons; Houston has the highest modelled evaporation refill cost before rainfall (City of Houston, Houston Public Works).

Newsroom kit

Quotable results

  • An uncovered 15 x 30 ft pool in Las Vegas, NV loses a modelled 23,444 gallons a year to evaporation, the most of 25 US cities (NOAA pan data, 1956 to 1970). (NOAA National Weather Service)
  • Modelled pool evaporation across 25 US cities ranges from 37.4 inches a year in Nashville, TN to 83.6 inches in Las Vegas, NV. (NOAA National Weather Service)
  • Replacing a year of pool evaporation costs $368.85 in Houston, TX and $26.68 in Sacramento, CA at rates in effect in October 2026 (modelled, before rainfall). (Pool Construction & Service)
  • Normal 1991 to 2020 rainfall equals or exceeds annual pool evaporation in 8 of 25 US cities studied. (NOAA National Centers for Environmental Information)
  • Only 15% of US pool owners have and regularly use a pool cover, according to the 2016 Residential End Uses of Water study cited by EPA in 2022. (U.S. Environmental Protection Agency)
  • Denver, CO loses 54.8% of its annual pool evaporation outside its 80F swim season (modelled). (Pool Construction & Service)

Primary sources to cite

Summary for media

An uncovered residential pool in Las Vegas loses about 83.6 inches of water a year to evaporation, more than twice the 37.4 inches lost in Nashville, according to a Pool Construction & Service model built on NOAA evaporation data for 25 US cities. For a 15 x 30 ft pool that is 23,444 gallons in Las Vegas and 10,485 in Nashville. Priced at water and sewer rates in effect in October 2026, replacing a year of evaporation costs from $26.68 in Sacramento to $368.85 in Houston, where sewer is billed on every gallon. Normal rainfall changes the picture: in 8 of the 25 cities, rain equals or exceeds annual evaporation, and the median refill cost after rain falls to $31.51. EPA says a cover can prevent up to 95% of evaporation, yet only 15% of owners use one regularly. The NOAA baseline from 1956 to 1970 matched newer Texas and Oklahoma estimates within 5%.

Headlines the model supports

  • Las Vegas pools lose 23,444 gallons a year to evaporation, the most of 25 US cities
  • Houston pool owners pay $368.85 a year to replace evaporated water, the most of 25 cities studied
  • Rain replaces most pool evaporation in 8 of 25 US cities, NOAA-based model finds
  • Denver pools lose 54.8% of their evaporation after swim season ends
  • Only 15% of pool owners use a cover regularly, though EPA says covers block up to 95% of evaporation

Cite this model

Pool Construction & Service. "Pool Evaporation Rate by City: Inches, Gallons and Refill Cost in 25 US Cities." PC&S Research Desk, October 7, 2026. https://poolconstructionandservice.com/research/pool-evaporation-rate/

License

The data tables and charts in this report are licensed under CC BY 4.0. Reuse them with this attribution: “Source: Pool Construction & Service (poolconstructionandservice.com), Pool Evaporation Rate by City: Inches, Gallons and Refill Cost in 25 US Cities.” Figures from third-party sources remain subject to their publishers’ terms.

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Evidence tiers

Tier 1: primary and government sources (39)

Tier 2: trade bodies, public companies, market research (2)

Tier 3: journalism and expert commentary (1)

Sources

  1. NOAA National Weather Service. NOAA Technical Report NWS 34: Mean Monthly, Seasonal, and Annual Pan Evaporation for the United States (Farnsworth and Thompson, December 1982). Accessed 2026-10-07.
  2. NOAA National Weather Service. NOAA Technical Report NWS 33: Evaporation Atlas for the Contiguous 48 United States (Farnsworth, Thompson and Peck, June 1982). Accessed 2026-10-07.
  3. NOAA National Centers for Environmental Information. U.S. Climate Normals 1991-2020, monthly station files (MLY-PRCP-NORMAL). Accessed 2026-10-07.
  4. Western Regional Climate Center (DRI, NOAA Regional Climate Center). Monthly average pan evaporation, comparative table (Western states). Accessed 2026-10-07.
  5. Texas Water Development Board. Lake Evaporation and Rainfall: quadrangle gross lake evaporation, data through December 2025. Accessed 2026-10-07.
  6. Oklahoma State University Extension. Evaporation Losses from Shallow Water Bodies in Oklahoma (BAE-1529, October 2016). Accessed 2026-10-07.
  7. Oklahoma Climatological Survey. Oklahoma Climate: climate divisions map. Accessed 2026-10-07.
  8. City of Mesa, Arizona. Is Your Pool Leaking? (pool evaporation chart, 400 sq ft pool). Accessed 2026-10-07.
  9. U.S. Environmental Protection Agency. Pool Water Efficiency (WaterSense). Accessed 2026-10-07.
  10. U.S. Environmental Protection Agency. Jump Into Pool Water Efficiency (EPA-832-F-22-015, September 2022). Accessed 2026-10-07.
  11. U.S. Environmental Protection Agency. How We Use Water (WaterSense). Accessed 2026-10-07.
  12. U.S. Department of Energy. Swimming Pool Covers (Energy Saver), archived capture of 2025-01-10; live page returned HTTP 404 on 2026-10-07. Accessed 2026-10-07.
  13. Town of Flower Mound, Texas. Pool Evaporation (utility billing guidance). Accessed 2026-10-07.
  14. Olivenhain Municipal Water District. Pool: Frequently Asked Questions. Accessed 2026-10-07.
  15. Latham Pool Products. My Swimming Pool is Losing Water: Is It Evaporation or a Leak? (June 16, 2024). Accessed 2026-10-07.
  16. Pool Construction & Service. Cost to Fill a Pool: water and sewer rate ledger, 25 US cities (rates in effect 2026-10-04). Accessed 2026-10-07.
  17. Pool Construction & Service. Pool Season Length by City (NOAA 1991-2020 daily normals, 60 metros). Accessed 2026-10-07.
  18. Albuquerque Bernalillo County Water Utility Authority (ABCWUA). Water rate schedule (ABCWUA Water and Sewer Rate Ordinance O-26-1 (approved)). Accessed 2026-10-04.
  19. City of Atlanta Department of Watershed Management (DWM). Water rate schedule (Water and Sewer Rates (DWM)). Accessed 2026-10-04.
  20. Austin Water (City of Austin). Water rate schedule (Rates and Fees | Austin Water). Accessed 2026-10-04.
  21. Charlotte Water (City of Charlotte). Water rate schedule (Rates & Fees, Charlotte Water (FY27 current rates)). Accessed 2026-10-04.
  22. Dallas Water Utilities (City of Dallas). Water rate schedule (DWU Monthly Payment Rates, effective October 1, 2026). Accessed 2026-10-04.
  23. Denver Water (Denver Board of Water Commissioners). Water rate schedule (2026 Residential Water Rates | Denver Water). Accessed 2026-10-04.
  24. Fort Worth Water (City of Fort Worth Water Department). Water rate schedule (Water and wastewater rates - City of Fort Worth). Accessed 2026-10-04.
  25. City of Fresno Department of Public Utilities, Water Division. Water rate schedule (City of Fresno Master Fee Schedule, Public Utilities Department (Amendment #590, all fees effective 07/01/2026)). Accessed 2026-10-04.
  26. City of Houston, Houston Public Works (Houston Water). Water rate schedule (2026 Water & Wastewater Rates (City of Houston)). Accessed 2026-10-07.
  27. Las Vegas Valley Water District (LVVWD), with Southern Nevada Water Authority (SNWA) charges. Water rate schedule (Water rates | Las Vegas Valley Water District). Accessed 2026-10-07.
  28. Los Angeles Department of Water and Power (LADWP). Water rate schedule (Schedule A - Residential (LADWP)). Accessed 2026-10-04.
  29. Miami-Dade Water and Sewer Department (WASD), retail. Water rate schedule (Rates, Fees and Charges (WASD)). Accessed 2026-10-04.
  30. Metro Water Services (Metropolitan Government of Nashville and Davidson County). Water rate schedule (Water, Sewer and Stormwater Rates (Metro Water Services)). Accessed 2026-10-04.
  31. Sewerage and Water Board of New Orleans (SWBNO). Water rate schedule (Rates, Fees & Charges (SWBNO)). Accessed 2026-10-04.
  32. City of Oklahoma City Utilities Department. Water rate schedule (Utilities Rates & Fees | City of OKC). Accessed 2026-10-04.
  33. Orlando Utilities Commission (OUC). Water rate schedule (OUC Service Rates & Costs). Accessed 2026-10-04.
  34. City of Phoenix Water Services Department. Water rate schedule (Water and Sewer Rates | City of Phoenix). Accessed 2026-10-04.
  35. City of Raleigh, Raleigh Water (Public Utilities). Water rate schedule (Public Utilities Rates, Effective July 1, 2026). Accessed 2026-10-04.
  36. Riverside Public Utilities (City of Riverside). Water rate schedule (Schedule WA-1A Single-Family Residential Metered Service). Accessed 2026-10-04.
  37. City of Sacramento Department of Utilities. Water rate schedule (Exhibit A Water Service Fees and Charges (rates effective July 1, 2016 to July 1, 2019)). Accessed 2026-10-07.
  38. Salt Lake City Department of Public Utilities. Water rate schedule (FY27 Rates | Public Utilities). Accessed 2026-10-04.
  39. San Antonio Water System (SAWS). Water rate schedule (Residential Water & Sewer Rates - SAWS). Accessed 2026-10-04.
  40. City of San Diego Public Utilities Department. Water rate schedule (Water Billing Rates (City of San Diego)). Accessed 2026-10-04.
  41. City of Tampa Water Department (City of Tampa Utilities billing). Water rate schedule (Residential Water and Wastewater Rate Schedule, Effective October 1, 2026). Accessed 2026-10-04.
  42. Tucson Water (City of Tucson). Water rate schedule (Residential Water Bill | City of Tucson). Accessed 2026-10-04.