Swimming Pool Evaporation Calculator
Estimate water loss, costs, and refill requirements accurately.
0
Gallons
Weekly Level Drop (Inches)
Monthly Loss (Gallons)
Rate (lbs/ft²/hr)
| Time Period | Water Loss (Gallons) | Level Drop (Inches) | Est. Weight (lbs) |
|---|
*Values assume constant environmental conditions.
Comparison: Current Conditions vs. Covered Pool vs. High Wind (10mph)
What is a swimming pool evaporation calculator?
A swimming pool evaporation calculator is a specialized tool designed for pool owners, maintenance professionals, and facility managers to estimate the rate at which water is lost from a swimming pool due to phase change from liquid to gas. Unlike simple volume calculators, this tool considers complex thermodynamic variables including water temperature, ambient humidity, and wind velocity.
Understanding pool water loss is critical for distinguishing between natural evaporation and structural leaks. If your actual water loss significantly exceeds the calculator’s estimate, you may have a plumbing leak or a crack in the pool shell.
Who Should Use This Tool?
- Homeowners: To budget for water bills and chemical adjustments.
- Pool Technicians: To perform bucket tests digitally and diagnose leak issues.
- Hotel Managers: To estimate operational costs for large commercial pools.
Swimming Pool Evaporation Calculator Formula
The calculation of evaporation involves determining the saturation vapor pressure at the water surface versus the partial vapor pressure of the air above it. The difference drives the evaporation, which is then accelerated by wind.
This calculator utilizes a variation of the standard engineering formula often derived from ASHRAE guidelines:
E = (C + 0.041 × V) × (Pw – Pa) × A
| Variable | Description | Typical Unit |
|---|---|---|
| E | Evaporation Rate | Gallons/Hour |
| V | Wind Velocity at Surface | MPH |
| Pw | Saturation Vapor Pressure (Water) | Inches of Mercury (inHg) |
| Pa | Saturation Vapor Pressure (Air Dew Point) | Inches of Mercury (inHg) |
| A | Surface Area | Square Feet ($ft^2$) |
Practical Examples (Real-World Use Cases)
Example 1: Summer in Phoenix (High Evaporation)
A standard 16×32 ft pool (512 sq ft) in hot, dry conditions.
- Water Temp: 84°F
- Air Temp: 100°F
- Humidity: 20%
- Wind: 5 MPH
Result: This pool could lose over 150 gallons per day. Over a week, that is more than 2 inches of water level drop, costing significantly in water replacement and chemical re-balancing.
Example 2: Covered Pool in Florida (Low Evaporation)
The same size pool (512 sq ft) but with a solar cover.
- Water Temp: 80°F
- Air Temp: 85°F
- Humidity: 70%
- Activity Factor: Covered (0.1)
Result: Evaporation drops drastically to roughly 5-10 gallons per day. Using a solar cover is the single most effective way to retain water and heat.
How to Use This Swimming Pool Evaporation Calculator
- Enter Surface Area: Multiply the length by the width of your pool. For irregular shapes, estimate the average average width.
- Input Temperatures: Measure the water temperature with a thermometer. Use a weather app for current air temperature.
- Set Humidity & Wind: These environmental factors significantly impact how “thirsty” the air is. Higher wind and lower humidity increase evaporation.
- Select Activity/Cover: Choose “Covered” if you use a solar blanket. Choose “Active” if the pool has waterfalls, fountains, or heavy swimmer use (agitated water evaporates faster).
- Analyze Results: Compare the “Weekly Level Drop” to what you see on your skimmer faceplate.
Key Factors That Affect Evaporation Results
Several variables influence the rate of water loss in your swimming pool system:
- Vapor Pressure Deficit: The greater the difference between water vapor pressure and air vapor pressure, the faster evaporation occurs.
- Wind Speed: Wind sweeps away the moist layer of air sitting just above the water surface, allowing dry air to take its place and absorb more water.
- Water Temperature: Warm water molecules are more energetic and escape the surface more easily. Heating a pool without a cover is a primary cause of massive evaporation.
- Humidity: In 100% humidity, evaporation is near zero because the air is saturated. In arid climates, evaporation is rapid.
- Surface Area: A wide, shallow pool loses water faster than a deep, narrow pool of the same volume.
- Agitation (Water Features): Fountains, spillways, and splashing swimmers increase the effective surface area, accelerating evaporation.
Frequently Asked Questions (FAQ)
On average, a pool loses about 1/4 inch of water per day, or 1.5 to 2 inches per week. However, extreme heat and wind can double this amount.
Yes. A solid or solar bubble cover can reduce evaporation by up to 95%. It acts as a vapor barrier, keeping moisture in the pool.
Perform the “Bucket Test”. Fill a bucket with water, place it on the pool steps (partially submerged). Mark the water level inside the bucket and outside (pool level). After 24 hours, if the pool level dropped more than the bucket level, you likely have a leak.
If the pool is heated and the night air is cool and dry, the temperature difference creates a strong vapor pressure gradient, causing “steaming” or rapid evaporation.
The “Active / Exposed” setting accounts for some agitation, but heavy splash-out from cannonballs or diving is physical water removal, not evaporation, and is hard to quantify exactly.
Yes. Indoor pools usually have low wind (0-1 mph) but humidity control is vital. High evaporation indoors can lead to mold and structural damage.
When water evaporates, solids (calcium, salt, cyanuric acid) stay behind. Only pure water leaves. This increases the concentration (TDS) of the remaining water, potentially causing scaling.
It can be. If you heat your pool in winter, the difference between the hot water and cold dry air causes very rapid evaporation unless covered.
Related Tools and Internal Resources
- Pool Volume Calculator – Calculate total gallons based on dimensions.
- LSI Calculator – Check your water balance and saturation index.
- Pump Turnover Calculator – Determine optimal filtration schedules.
- Chemical Dosage Charts – How much chlorine or acid to add.
- Pool Heating Cost Estimator – Calculate the energy cost of warming your pool.
- Salt Water Generator Sizing – Find the right cell size for your evaporation rates.