How Much Water Will A Pool Lose To Evaporation

Chris has a Main's caste in technology and uses his knowledge to write nearly a variety of topics from an analytical perspective.

Left unchecked, evaporation affects a pool's chemical balance and the integrity of the pumping and filtration systems. — Left unchecked, evaporation affects a pool'south chemical rest and the integrity of the pumping and filtration systems.

SuperFantastic, CC-By 2.0, Flickr

According to the National Swimming Pool Foundation, there are over 10 one thousand thousand swimming pools in the United States. That means there are virtually 160 billion gallons of water available for pond, or roughly ane pool for every 31 people in America!

If you're reading this, there is a pretty good run a risk that you have a pool in your backyard (or are thinking near getting one). As you may already know, a pool is a large investment and requires lots of planning and ongoing maintenance to ensure that it tin provide yous and your family with years of enjoyment.

Why Puddle Evaporation Matters

1 often overlooked issue is how much water you would wait to lose due to evaporation in whatsoever given year. Depending on where you alive, an boilerplate-sized residential puddle with a surface area of 400 square feet could lose equally much equally 10,000 gallons of h2o each twelvemonth due to evaporation! If left unchecked, evaporation tin can affect the pool's chemic residue also as the integrity of the pumping and filtration systems. Of course, this will likewise end up costing yous money too! Given this proffer, it is a worthy investment of time to gauge just how much water your puddle could lose to evaporation each year.

3 Ways to Measure out Pool Evaporation

Direct measure
Estimate using evaporation rate maps and data
Calculate using mathematical equations

Straight Measure the Evaporation

If you already take a puddle, the easiest way to effigy out how much h2o you are losing is to measure it straight. Measuring the evaporation rate is relatively simple.

Start, begin past using a ruler or record measure to measure the distance from the pool deck to the water's surface. Also, notation the appointment that this initial measurement was taken. After about a week employ the ruler or tape measure out to measure the distance again. Brand sure that you accept the measurement at the same location as before. At this point, you should have a vertical distance and an elapsed time. If y'all divide the altitude by the elapsed time, the result will exist the charge per unit of water loss (evaporation).

To convert this evaporation rate into gallons lost over a specific fourth dimension period, you will need to catechumen the measure into a volume. For example, if your measurement was in inches per day, simply divide that by 12 to convert information technology to feet per day. Next, multiply that value by the surface expanse of your puddle and and then by seven.48 to get gallons per 24-hour interval.

If you don't have a pool to measure out the evaporation charge per unit, yous can simply apply the same method stated above to whatsoever container that can concord water for an extended period of time.

This is a global evaporation map. South America experiences the most evaporation out of any region.

Centre for Ecology and Hydrology, at Wallingford in the Uk

Estimate Using Evaporation Charge per unit Maps and Data

If y'all tin locate an evaporation rate map for your area, y'all can hands calculate the corporeality of water that would be anticipated to evaporate from your puddle. Most maps that are available to the public volition written report evaporation rates in units that aren't necessarily intuitive to use, such as millimeters per month. Subsequently doing some simple unit conversions, yous volition have an evaporation rate that is useful.

The National Weather Service's Climate Prediction Heart is a good source for evaporation maps for the United States. Some state governments and organizations have their own evaporation data and maps as well. Cheque with your state water resource sectionalization or local university for more data. For example, the Western Regional Climate Center has a bully data set up that can be used for estimating evaporation for my part of the country. I used this data for my analysis shown at the terminate of this commodity.

For an even easier and quick approximate, many people suggest using a linear loss rate of 0.25 inches of h2o per day during the summertime. Using this rule of thumb, a typical 500 square foot puddle may lose about 78 gallons of water per day.

Summate Evaporation Using Mathematical Equations

In reality, evaporation is a very complex process that is difficult to approximate using equations. This is considering the rate of evaporation is actually controlled by many factors including, temperature, air pressure, current of air speed, and humidity. Several equations exist that can exist used to predict evaporation. Beneath I will highlight some of the more than well-known ones. Delight note that I have modified these equations to eliminate constants and to make the units consequent with the intent of this article. Backup documentation (and the original format and units) for each of these methods is noted in the reference section at the terminate of this article.

Delight annotation that these equations won't necessarily be accurate plenty to determine the ventilation needs of an indoor pool. If this is your intent, delight read the latest resources and publications from The American Society of Heating, Refrigerating and Air conditioning Engineers for guidance on this specific issue.

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Then How Much Water Does a Typical Pool Lose?

The boilerplate American in-ground pool measures about 14ft by 28ft and has a depth of four.0ft to 6.5ft deep. This results in an outcome swimming surface expanse of 392 foursquare feet. Using the equations from higher up and weather from a typical summertime 24-hour interval in Arizona, I compute the following numbers:


	Rule of Thumb (1/iv" per day)	Evaporation Map/Information	EPA Equation	Stiver & Mackay Equation	Lund Equation
Gallons/Day	61.0	63.2	83.0	17.2	98.6
Gallons/Yr	22,297	23,056	30,309	half-dozen,264	35,983

My son's wading pool lost 1.4 inches (about 44 gallons) of water in a week. — My son's wading pool lost 1.4 inches (about 44 gallons) of h2o in a calendar week.

CWanamaker

Comparison of Methods on My Son'southward Small Pool

I've done my ain experiment and compared my observations with the results of the in a higher place three equations likewise as the results of an evaporation map. My son's eight-pes bore pool lost about 1.iv inches of water in a one-calendar week catamenia.

Below is a table summarizing the evaporation rate for my lawn located in Phoenix, Arizona. I used data from our conditions reports to determine the parameters for the equations.


	Straight Measure out	Evaporation Map/Information	Rule of Thumb (1/iv" per day)	EPA Equation	Stiver & Mackay Equation	Lund Equation
Gallons/Day	six.3	8.1	7.8	9.vi	ii.4	five.0
Gallons/Twelvemonth	2,285	2,957	2,859	3,513	890	1,836

Last Thoughts

As you tin see, the use of these methods produce some slightly varied results. While straight measurement will produce an accurate evaporation rate specific to an area, it doesn't accept into account seasonal variations in temperature, pressure level, and humidity. Extrapolating that result to compute the amount of water lost in a year could be simply as inaccurate as any of the other methods.

So which method should be used? Well, the use of any method is predicated on the reason for which the interpretation is needed. I believe that in most outdoor residential applications, interpretation using actual data/maps will serve to come across the purposes of the puddle owner. For that matter, the simple rule of thumb of 1/4" of h2o loss per day can fifty-fifty be a uncomplicated and adequately accurate way to estimate evaporation loss. In the end, though nosotros must proceed in mind that what we are shooting for is an estimation of evaporation based on an average of predictable conditions.

References and Resources

Beychock, Milton. "Fundamentals of Stack Gas Dispersion." July six, 2012.

Jensen, Marvin E. "Estimating Evaporation from Water Surfaces." March 2010.

Lund, John W. "Design Considerations for Pools and Spas (Natatoriums)." Oregon Institute of Technology Geo-Heat Center. 2000.

This article is authentic and true to the best of the author's knowledge. Content is for advisory or entertainment purposes only and does not substitute for personal counsel or professional advice in business organization, financial, legal, or technical matters.

Questions & Answers

Question: When you lot mention a puddle loses ane/four" of water per day, does "per day" mean a menstruum of 12 or 24 hours?

Answer: The one/4" per mean solar day rule refers to a 24-60 minutes period. Much of the evaporation will occur during the 24-hour interval due to the presence of the sun. However, you lot will withal have water loss during the dark as well.

JOHN ROSWELL on July 29, 2020:

Dew signal temperature is not considered in these formulas. In much of the country/world summers are humid. If the night temperature is beneath the dew signal, won't this limit the amount of absorption of the puddle vapor into the air?

Arturo on December 12, 2019:

How much evaporation tin be expected from a 600 sq ft pool heated at 94 degrees

Location. San diego ca

Air temp day mid lxx'due south

Dark temp low 50's

No puddle cover

Abdullah Alyami on Baronial 30, 2019:

I'one thousand calculating the evaporation rate for a large pool in the Bay Area, California and the pool would be heated 18hr per month. when I use the EPA equation, does it have the time embedded in it to be per twenty-four hours? Is it calculating the evaporation per 24-hour interval? I noticed it doesn't say anything about fourth dimension in the equation.

sothon on August 25, 2019:

why when temperature go smaller, it volition issue in larger evaporation rate?

john letendre on August 22, 2019:

How much water should I wait to loose on a pool 20' x 33' that has a vanishing edge (water washing into a spill fashion trough) that is 33' long. I would like worst instance, so summer fourth dimension with out side temp of ninety degrees. Pool water at ambient temp (no heating)

Mike Patterson on June 20, 2019:

Note that if you don't live in Arizona and take to estrus your puddle, evaporation is the main heat loss mechanism. Roofing your pool when it is not in use will save you a pregnant corporeality of coin and reduce your greenhouse gas emission.

David Atherton on February 13, 2019:

This article is one of the strongest arguments I have always seen for the US to go metric. Can you imagine how much the The states economy would benefit if everyone could do this kind of stuff in their head in seconds.

roy h. on Jan 10, 2019:

great article for all of us pool owners its not a leak its evaporation.to check for leak use a 5 gallon saucepan place it on one of your steps fill up with water up to the water level of your pool mark that whith a little line if the pool and the water in the bucket drop identically you don't have leak if pool drops quicker than bucket phone call for service.thanks.

Marc on August 17, 2018:

Using the calculation, what will be the evaporation loss of 140,000 acre feet of water (California) (based on the online calculator it translates to roughly 45 billion gallons of h2o}. How many gallons of water will exist lost to evaporation? Thank you for your response.

Christopher Wanamaker (writer) from Arizona on Apr xvi, 2018:

Robert,

For 45 miles of restored river, the evaporation would indeed be significant. In the Tempe/Phoenix area we tin can expect to have about 100 inches of evaporation per year. Assuming that the river spans an average width of 875 Feet (which represents the gauge width of Tempe Boondocks Lake) yous would have i,732,500,000 cubic anxiety of h2o evaporating each yr. This is equivalent to 12,960,000,000 gallons per twelvemonth or about 35,506,849 gallons per day.

Thanks for reading!

Robert Smart on April 04, 2018:

So and so, with the announcement today on LinkedIn past ASU of the "Rio Remagined" Common salt River projection of 45 miles of h2o in the river basin, how much h2o will take to be used each twenty-four hour period to go on that filled after the furnishings of evaporation? What proportion of the full h2o utilise in the surface area does that correspond. Despite the name "Smart," I'll have to leave information technology upwards to y'all to calculate. The project sounds really cool, just wow that has to be a huge consumptor of water - just through evaporation. No one in the proclamation addressed that. I love these types of projects that bring communities together, but the evaporation result HAS to be considered. Forty-five miles of water surface exposed to the Arizona temper. That's a lot of area.

roy h on Jan 25, 2018:

overnice resources to find out where is the water going. I have a 30 x 15 inground with screen enclosure I take tiles around the recommended make full level that has dots in a dimond shape I use a garden hose about evert ix to 10 days measured output is 9 gal per min. for 1 hour 540 gal in hour brings it up to fill up dot.it is 60 gal day or direct mensurate is accurate.about 1600 gal.per calendar month cost is less than $20/mo.in due east coast of fla. hope this helpl the less mathamatisionswe have on lath

GP on August 03, 2017:

Or yous tin can average all the methods and y'all get almost the aforementioned result of the accurate direct method.

George F. on July 25, 2016:

Very worthwhile presentation of an everyday curiosity by an average pool owner. Information technology's good to run into a little science involved in 1 of our fun sides of life.

Joanie Ruppel from Keller, Texas on November 05, 2015:

A very interesting hub for pool owners pondering the evaporation rate that besieges us always!

Kristen Howe from Northeast Ohio on April xvi, 2015:

CWanamaker, this was a real interesting hub nearly swimming puddle water evaporation. It would give you something tot think about. Voted up for interesting!

Ejikeme Nzeka on April 18, 2013:

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swimfan from The states on January 26, 2013:

Nice, thorough article that definitively covers the subject of pool water evaporation. Thanks.