Anyone who’s owned or maintained a pool knows how rapidly water levels can drop. According to the Environmental Protection Agency, a typical uncovered pool can lose between 12,000 and 31,000 gallons of water annually, simply due to evaporation.

Here’s what can be done to preserve the water you’ve already paid for!

Cover It Up

The most effective way to prevent evaporation is to put a lid on top of the pool, effectively keeping pool water locked in. The same EPA report tells us a pool cover can prevent up to 95 percent of evaporation. Pool covers also help retain heat, so heated pools that are covered use less energy to maintain their temperature. And because covers prevent dirt and foreign objects from entering the pool, you’ll find yourself adding fewer chemicals over time.

The biggest downside of a pool cover? It’s easy to forget to use it. Or you just don’t feel like putting the cover on that night. And to be clear, some covers are bulky and difficult to deploy by yourself. Automated covers are an option, but many pool owners balance cost and practicality by rotating two sets of covers: a heavy one that stays on between pool seasons, and a lightweight cover for the summer months.

Liquid Protection

Liquid Evaporation Suppressants (LESs) are less effective than a full pool cover, but are affordable and extremely easy to use. They create an invisible film on top of the water that effectively seals the pool and reduces evaporation.

Pool owners love this product because they simply put it in and forget it, except to top it off from time to time. However, LESs aren’t as effective as a physical cover and don’t stop dirt and debris from falling into your backyard pool.

Turn Down the Heat

If you own a heated pool, consider lowering the heat at night. Evaporation is affected far less by the temperature outdoors, and more by the difference in temperature between the pool and the air around it. Most pools are approximately the same temperature as the air during the day, but evaporation rates soar at night when the hot water and cold air vary greatly. (That’s right, most pool evaporation occurs at night!)

If you’ve ever used a pool at night, you’ve likely seen steam rising from the water. That steam is evaporation, and it’s money slipping out of your pocket.

Structures to Shade and Stop the Wind

On a hot and sweaty day, nothing brings relief like a cool breeze. That sensation is your sweat evaporating, accelerated by the moving air. Outdoor breezes work in exactly the same fashion on your below- or above-ground pool, enhancing evaporation and dropping your water levels even lower.

Structures and large plants such as pergolas, shade trees, fences and bushes block the sun and break up the breeze. That keeps your pool water where it belongs — in the pool!

Shade has a secondary benefit as well, helping to keep the chlorine levels higher than if exposed to direct sunlight. Generally, evaporation contributes little to the loss of pool chemicals or stabilizers such as chlorine or salt. But direct sunlight can break apart the chlorine in your pool, transforming it into a gas that escapes. Many pools use a stabilized form of chlorine to reduce evaporation due to UV rays, but shade structures or trees can make a big difference as well.

If you’d like to read more about pool water evaporation and retention, the EPA’s WaterSense initiative released a 22-page report in 2018 that dives into this issue.