Swimming Pool Evaporation Calculator: Is Water Loss Normal in Atlanta?

Your pool water level is dropping, and you are not sure whether it is just the Atlanta summer doing its thing or something more serious happening underground. That gap between "probably fine" and "this is costing me money" is exactly where most pool owners in Roswell, Alpharetta, and Johns Creek get stuck every July.

Atlanta Leak Pros has spent 13 years working on residential pools across the North Atlanta metro, and the team sees this question every week during the summer months. The difference between evaporation and an active leak is not always obvious, but the right information makes it a straightforward call.

Keep reading to find out how a swimming pool evaporation calculator works, what inputs you need for accurate Atlanta-area results, how to interpret the numbers, and when the math points to a real problem rather than normal water loss. 

How Pool Water Loss Happens

Every uncovered pool loses water every day. The only question is how much, and whether that number matches what evaporation physics would predict or exceeds it.

Evaporation vs. Hidden Leaks

Evaporation is a surface process. Water molecules at the pool's surface absorb heat, convert to vapor, and escape into the air. It is continuous, predictable, and measurable. A hidden leak is a structural or plumbing failure that removes water from the pool in a separate, additional stream. 

The two can happen simultaneously, which is why comparing your actual water loss to a calculated evaporation estimate is the right starting point.

In Atlanta summers, an uncovered pool with average exposure can lose between a quarter inch and three-quarters of an inch of water per day to evaporation alone. That translates to roughly 130 to 400 gallons per day for a standard 15-by-30-foot pool. If your pool is losing significantly more than the calculator predicts for your conditions, that gap is the number worth paying attention to.

Why Surface Area and Weather Matter

The larger your pool's surface area, the more water is exposed to air at any given moment. A freeform pool with a large shallow beach entry will lose more water per hour than a narrow lap pool of equal volume. Surface area is the single biggest variable in any evaporation estimate, and it is the first number every calculator asks for.

Beyond size, the four weather conditions that drive evaporation are air temperature, water temperature, relative humidity, and wind speed. Low humidity pulls vapor away from the surface faster. 

Wind continuously replaces saturated air above the pool with drier air, accelerating loss. High water temperature raises the vapor pressure differential between the water and the air above it, pushing more molecules into the atmosphere. None of these factors operate in isolation, which is why a simple rule of thumb gives a less reliable result than a full calculator input.

Knowing what drives evaporation naturally leads to the next question: exactly what do you enter into the calculator to get a result that reflects your specific pool and zip code?

What to Enter Into the Calculator

A swimming pool evaporation calculator is only as accurate as the inputs you give it. Rounding up your pool dimensions and pulling current weather data from a weather app takes about five minutes and produces a meaningful result.

Pool Dimensions and Water Surface

The calculator needs your pool's surface area, which is the length multiplied by the width for a rectangular pool. For kidney or freeform shapes, most calculators offer a shape approximation option, or you can use the square footage listed in your original build documents. What you do not need is the pool's volume or depth; evaporation happens at the surface, not throughout the water column.

If your pool has a spa that shares water with the main pool, add the spa's surface area to the pool's surface area. The spa typically runs at a higher temperature than the pool, and its smaller surface evaporates at a higher rate per square foot. Leaving it out will underestimate your total expected loss.

Temperature, Humidity, and Wind Exposure

For water temperature, use an actual thermometer reading rather than your thermostat setting, especially if the heater has not run recently. Air temperature should reflect the daytime average during the period you are measuring, not the overnight low. 

Relative humidity data is available from any weather app; for Alpharetta and Roswell specifically, mid-summer afternoon humidity often sits between 55 and 70 percent, which is moderate but not enough to dramatically slow evaporation when temperatures exceed 90 degrees.

Wind exposure is often the most underestimated input. A pool in an open backyard with afternoon westerly breezes will evaporate measurably faster than one tucked behind a privacy fence or surrounded by mature trees. 

Most calculators categorize wind exposure as low, moderate, or high rather than asking for a precise miles-per-hour figure. Choose the category that best reflects your actual yard conditions, not the regional wind average.

Once you have run the numbers, the next challenge is knowing whether the result your calculator returns indicates everything is fine or signals that something else is going on.

How to Read the Results

The calculator's output is a predicted loss rate, typically expressed in inches or gallons per day, based solely on evaporation physics. Your job is to compare that number to your observed water loss.

Expected Daily and Weekly Drop

For most Atlanta-area pools in July, a calculator using accurate local inputs will return a daily evaporation figure somewhere between 0.2 and 0.75 inches. On the high end of that range, that is roughly half an inch per day in full sun, with afternoon breezes and water temperatures around 85 degrees. 

Over a week, that amounts to a 1.5 to 5-inch drop in water level, which is a wide range but still within normal bounds depending on your specific conditions.

If your pool has not had rain and you measure the water level drop over 24 hours using a fixed reference point on the pool wall, that number should fall within 20 to 30 percent of the calculator's output. Minor differences are normal because real-world conditions fluctuate. A result that lands within that margin means evaporation is likely the full explanation.

When the Numbers Look Too High

If your measured drop is consistently 50 percent or more above the calculator's predicted evaporation, that gap points to a second source of water loss. The most common culprits are active plumbing leaks, shell cracks, fitting leaks around returns or skimmers, and equipment-side leaks at the pump or filter. 

A one-inch-per-day loss when the calculator predicts 0.4 inches is not a rounding error. It is a meaningful signal. Atlanta's clay soil adds a layer of complexity worth naming here. Clay expands and contracts significantly with changes in moisture, and during dry summers, the soil around a concrete pool can shift. 

That movement can stress underground plumbing lines and widen existing shell cracks over time. A loss rate that was normal two summers ago and has now increased deserves attention, especially if your yard has been dry for several weeks. The next logical step is to understand how local Atlanta conditions affect your evaporation rate, independent of any leak.

Atlanta Conditions That Speed Up Water Loss

Atlanta's climate creates above-average evaporation pressure on residential pools from May through September, and pool owners in the North Metro feel the effects every summer.

Summer Heat Across North Metro

Marietta, Roswell, Alpharetta, and Johns Creek all average high temperatures between 88 and 93 degrees Fahrenheit during peak summer months. Pool water in an unshaded yard can reach 85 to 90 degrees by mid-afternoon, significantly increasing the vapor pressure differential between the water surface and the air. The wider that differential, the faster water molecules escape.

Atlanta also sees periods of low overnight humidity that allow evaporation to continue through the night, unlike coastal climates where nighttime humidity often rises enough to slow the process. This means your pool can lose water around the clock during a typical Atlanta heat wave, not just during the hottest afternoon hours.

Sun, Breezes, and Pool Features

Direct sun exposure on the pool surface raises water temperature and drives evaporation independently of air temperature. A south-facing pool with no overhead shade will evaporate faster than a pool under a pergola or beside mature trees, even when the air temperature is identical. 

The sun's effect on water surface temperature is the variable most homeowners underestimate when they try to eyeball their evaporation rate.

Water features add another layer. Waterfalls, spillover spas, fountains, and bubblers all aerate the water as it moves through the air, converting liquid water to vapor before it even settles back into the pool. 

A decorative waterfall running for six hours per day can measurably increase your total daily water loss beyond what any standard evaporation calculator accounts for. If you are running water features and comparing your loss rate to a calculator that does not include them, your numbers will not match.

Ways to Reduce Unnecessary Evaporation

A pool cover is the single most effective step you can take. A quality solar or safety cover reduces evaporation by up to 95 percent when the pool is not in use.

Using Covers and Managing Splash-Out

Solar covers work by trapping a thin layer of warm, humid air between the cover and the water surface, which sharply reduces the vapor pressure differential that drives evaporation. They also absorb solar heat and transfer it to the water, which can extend your swim season. Automatic reel systems make covering and uncovering a pool fast enough that most homeowners actually use them consistently.

Splash-out is a separate but meaningful source of water loss that often goes untracked. A pool actively used by children can lose several inches per week from splashing alone, and that loss does not show up in any evaporation calculator. 

Tracking your water level on days with no pool use versus days with heavy activity helps separate splash-out from evaporation in your overall water budget.

Adjusting Water Features and Run Times

Limiting water feature run times to two or three hours during peak evening hours, rather than running them all day, reduces evaporation loss without sacrificing the visual effect. Running features after sunset is even more efficient because air temperatures are lower and humidity is higher, which slows evaporative loss from the aerated water.

Windbreaks are another practical option for exposed yards. Strategic placement of privacy fencing, landscaping, or shade sails along the prevailing wind direction can reduce effective wind exposure at the pool surface and meaningfully reduce evaporation without any changes to the pool itself. 

Once you have addressed what you can control, the remaining question is how to determine whether what remains is purely evaporation or a real leak.

When to Move Beyond the Estimate

The calculator gives you an expected evaporation rate. What it cannot do is tell you whether a specific crack, fitting, or plumbing line is adding to your water loss.

Using the Bucket Test for Confirmation

The bucket test is the most reliable low-tech method for separating evaporation from a leak. Fill a five-gallon bucket with pool water and set it on a pool step so it sits partially submerged. Mark the water levels inside the bucket and in the pool on the bucket's exterior. Wait 24 hours without using the pool, then compare the two drops.

If the pool water dropped more than the water inside the bucket, your pool is losing water beyond evaporation. The bucket experiences the same air temperature, wind, and humidity as the pool surface, so its internal evaporation mirrors what the pool would lose under normal conditions. A larger pool-side drop is a reliable signal that something else is happening.

Signs It Is Time to Schedule an Inspection

Use this list to decide when to move from testing to calling a professional:

• Your measured daily water drop exceeds the calculator's evaporation estimate by more than half an inch consistently
  
  
• The bucket test confirms the pool is losing more water than evaporation accounts for
  
  
• You notice wet spots on the deck, soft ground near equipment, or visible cracks near returns or skimmers
  
  
• Your water bill has increased without a clear explanation
  
  
• You are adding water two or more times per week during a period without heavy splash-out or rainfall

A calculator and a bucket test can confirm that something is wrong. They cannot locate where the problem is. Electronic and pressure-based detection equipment, operated by a trained technician, is the only reliable way to locate the source of a hidden leak before it causes further structural or plumbing damage.

Frequently Asked Questions

Your Pool Water Level Keeps Dropping — How Do You Calculate Normal Daily Evaporation Based on Temperature, Humidity, and Wind?

Enter your pool's surface area, current water temperature, air temperature, relative humidity, and wind exposure into a swimming pool evaporation calculator to get a daily estimate. For most Atlanta-area pools in summer, normal evaporation ranges from 0.2 to 0.75 inches per day, depending on those variables. Compare that figure to your actual measured loss to identify whether additional water is disappearing beyond what evaporation explains.

You're Losing About 1 to 2 Inches a Day — How Do You Tell if It's Evaporation or a Leak That Needs Pool Leak Detection?

Run the bucket test alongside a calculator estimate. If your pool drops consistently more than the bucket does over the same 24-hour period, that gap points to a structural or plumbing leak rather than evaporation. Losses above 1 inch per day in Atlanta summer conditions almost always exceed what evaporation physics can account for and warrant a professional pool leak-detection inspection.

You Want a Quick Reality Check — What's a Normal Amount of Pool Water Loss in 24 Hours in Atlanta-Area Weather?

For an uncovered residential pool in Marietta, Roswell, Alpharetta, or Johns Creek during July, a typical 24-hour loss ranges from a quarter inch to three-quarters of an inch. That equals roughly 130 to 400 gallons for a typical 15-by-30-foot pool. Anything consistently above that range in calm conditions is worth investigating.

You Use a Pool Cover — How Much Should Evaporation Drop, and When Does Ongoing Loss Point to an Underground Plumbing Repair?

A cover in regular use reduces evaporation by up to 95 percent, so a covered pool should show very little measurable water drop between uses. If your covered pool is still losing half an inch or more per day, evaporation is no longer the likely explanation, and underground pool plumbing leak detection becomes the appropriate next step.

You Need a Local Estimate — How Do You Factor Your ZIP Code's Weather Data Into an Evaporation Estimate for Your Pool?

Most online swimming pool evaporation calculators let you enter real-time temperature, humidity, and wind data directly, which you can pull from a local weather app using your ZIP code in Alpharetta, Roswell, or Johns Creek. Using local mid-afternoon conditions during a dry stretch gives you the most conservative estimate, because those are the hours when evaporation pressure peaks in the Atlanta metro.

You Want Numbers You Can Trust — What Inputs Do You Need to Estimate Evaporation From Pool Surface Area, Water Temperature, and Air Temperature?

The essential inputs are pool surface area in square feet, water temperature in Fahrenheit, air temperature in Fahrenheit, relative humidity as a percentage, and wind exposure level. With those five inputs, a calculator can apply vapor-pressure physics to produce a reliable daily evaporation estimate. Leaving out any one of them, especially wind exposure, typically results in an underestimate for open Atlanta-area backyards.

What the Numbers Are Telling You

A swimming pool evaporation calculator gives you a baseline, and that baseline is worth knowing. It turns an anxious guess into an informed comparison you can act on.

If your actual water loss matches the calculator's estimate, you can stop worrying and focus on reducing unnecessary evaporation by using a cover and adjusting run times. If your loss exceeds the estimate by a meaningful margin, you now have a concrete reason to take the next step rather than waiting to see if the problem gets worse. In Atlanta summers, problems that involve water loss rarely stay the same size.

Call Atlanta Leak Pros today and get a free estimate on your pool leak repair or renovation. The team has spent 13 years finding leaks and restoring pools across Marietta, Roswell, Alpharetta, and Johns Creek, and the process starts with a straightforward on-site inspection, not a guess.