Evaporation of Pool Water

Swimming Pool Evaporation: A Guide to Prevention

It comes as no surprise that pool leaks are a significant cause of water loss in your swimming pool. What you may be surprised at, though, is that while leaks are a major cause, they are not the number one cause. That honor goes to water evaporation.

According to the Department of Energy, swimming pools and spas lose up to 70% of water through evaporation. Leaks follow behind as the number two reason for water loss. For the purpose of water evaporation, let's examine possible reasons why this may be happening to your pool or spa.

Water loss through evaporation

We all know that evaporation is simply the process of liquid turning into vapor. So how does that make a difference for swimming pools? Well, evaporation occurs each time your pool is exposed to wind or air at the surface. In short, this is pretty much all the time, in every pool. Water at the surface will form into a vapor. Eventually, this vapor is released into the air.

Interestingly enough, it isn't even day time that you can lose the most heat. Heated pools on cool nights will experience evaporation more rapidly. This explains why most of a heated pool's heat is lost overnight. There are ways to fight evaporation, though.

Pools and Spas love to be covered when not in use

The best way to prevent evaporation is as easy as buying a pool or spa cover. Pool covers can actually reduce evaporation by up to 95%. That alone should be enough proof to get you to consider purchasing one if you haven't already. Aside from the water savings, there are other benefits to owning a pool cover.

Pool covers also keep and maintain pool warmth inside your pool. Remember earlier in the article; we mentioned losing heat in heated pools without a cover? Well, the cover will trap the heat inside the pool and will also reduce the energy demand on your pool equipment (lower your pool maintenance costs). Your new pool cover will also reduce the number of chemicals you are using, reduce pool debris, and will significantly reduce the amount of time your pump and filter will be used.

Water features need downtime as well

Cool water features like the waterfalls and jets are great and make a beautiful accent to your pool, but every once and awhile, turning them off will help prevent evaporation. Laminar jets and cascading waterfalls are the two big ones having the highest chance of contributing to water evaporation. It is recommended to turn them off when not in use. This will save you on water and chemicals anyway, and when you've got guests coming over, urn them on and have a great time.

Reduce your water temperature

You most likely have heard that warmer water evaporates faster than cooler water because the warmer water molecules move faster. Well, as temperatures drop, the warm water will evaporate even quicker. This process of evaporation is even quicker is the temperature of the pool water is higher than the air's temperature.

Cold water is a bit more resistant to evaporation, so keep this in mind if you're goal is to prevent evaporation and want to save money on water.

Signs you may be losing water to evaporation

One way to be sure to test if you're losing water to evaporation (or a leak actually as well) is to perform a water bucket test. Follow a structured approach to leak detection as described in the TFP Leak Detection article The bucket test as described in that article should be your first step to determine if water loss is from evaporation or a leak.

If, after examining the water levels, you see that the outside level is lower than the inside level, you most likely have a leak instead. Best to call a professional in at this point to verify if your pool is leaking.

Why Does Evaporation of Pool Water Happen?

Warm water with cold night air increases evaporation. On a very cold morning you will see fog rising from the pool.

You can lose 1/2" to 3/4" of water a day due to evaporation. The greatest evaporation rate can be in May and Sept/Oct in North America, when pool water can be in the 80's during the day and overnight air temps drop into the 70's.

Variations in wind intensity, humidity and sunlight can drastically change water loss rates. Some of the strongest and most intense wind in the country can be found in mountainous regions. The wind will undoubtedly have an effect on pool water, as wind can blow water particles and cause speedy evaporation. Other windy regions include the Great Plains, the Great Lakes and most coastal locations.

How to Reduce Evaporation in Pools

• Cover the pool. Research shows use of pool covers could reduce 95 percent of evaporation from California pools
• Reduce water temperature. Lower the thermostat on the pool heater. Reduce the difference between the pool water temperature and the nighttime air temperature.
• Add windbreaks around the pool. Landscaping, fences, or hedges can reduce the wind speed that hits the water surface.

I Am Losing Pool Water - Is it a Leak or Evaporation?

If your pool is only losing water in cooler months it is likely evaporation. We often see members thinking their pool sprung a leak when evaporation increases as the seasons change.

Follow a structured approach to leak detection as described in the TFP Leak Detection article The bucket test as described in that article should be your first step to determine if water loss is from evaporation or a leak.