Heated pools do result in more evaporation, so more make-up water is required to refill heated pools than unheated pools. Whether using solar heating, heat pumps, or gas heaters, heated pools do require more water.

But how much will the increase in water usage cost?

We have heard just about every question imaginable when it comes to solar pool heating. That’s a question we had not heard before, and it’s a great question! As a curious bunch, it got us thinking… and calculating.

Cost of Water Evaporation In Heated Pools

The answer is not easy, but we can come up with a reasonable guess based on experience. First, we have to consider that for about half of the year, no make-up water is required due to rain in Southwest Florida. During the other half of the year, every pool owner needs to add water to refill their pool. Many factors impact the amount of water required, including whether the pool is screened, covered, protected from wind, circulated at night, etc.

It also depends to what temperature you heat your pool. The calculation would be extremely complex.

The humidity and temperature difference between the ambient air and the pool surface impacts the rate of evaporation. On cold, dry nights, evaporation can be significant as seen in this video below.

What Does Excess Water Evaporation Really Cost?

Based on experience, on the absolute high side, you might expect to need an additional inch of water per week for a heated pool. We can calculate out how much water that would be for a sample 14’x28′ pool:

14 ft x 28 ft x 1/12 ft depth x 7.48gal/cf x 26 weeks per year = 6,350 gallons

So what does this cost? This is another “it depends” answer.

Lee County Utilities currently charges $3.27 for water in it’s lowest residential usage tier. So the annual cost would be about $21 per year on the absolute high side. However, if you are on municipal sewer, you would need to add this cost at $5.85 per thousand gallons, adding another $37 per year.

In reality, for someone on municipal water and sewer, the cost would be pretty low. We expect that the added water cost would be in the range of $20 per year for most pools if heated at all times.

How Can I Minimize Water Evaporation Costs?

These are probably grossly inflated costs. It is extremely unlikely that you would increase your water usage by 1 inch per week, half of the year. The figure is likely much less. But there are steps you can take to reduce evaporation in a heated pool:

• Only heat your pool when you actually plan to use it. If you always keep your pool warm you will need more make-up water. If you use electricity or gas, you are also throwing money out the window, quite literally.
• Cover your pool. Nothing does more to stop evaporation than a solar cover, especially during cool and dry conditions and especially at night when most evaporation usually occurs.
• Shelter your pool from wind. Wind increases evaporation dramatically.
• Minimize water features. Waterfalls, deck jets, and spa overflows
• Do not circulate your pool at night. This causes more warm water to reach the surface.