Can water still evaporate at night?

Does Water Evaporate from Pools at Night?

Many pool owners wake up to noticeably lower water levels and wonder—could evaporation really happen overnight? The answer is a definite yes. Even without sunlight, water continues to evaporate, especially when there's a sharp difference between the pool temperature and the cooler night air.

Here’s how it works: warm water releases moisture more readily into colder, drier air. For example, a heated pool maintained at 88°F on a night when the air drops to 50°F creates ideal conditions for evaporation. That temperature gap drives moisture from the surface upward, where it’s carried away by airflow—sometimes resulting in the loss of 1 to 3 inches of water in just one night.

Heated pools are especially vulnerable. Because they maintain a higher surface temperature, they lose more water after dark than unheated ones. This effect is strongest in spring and fall, when daytime warmth gives way to chilly evenings. Wind can amplify the process, pulling vapor away faster and allowing more water to evaporate in its place.

While rain or high humidity can slow evaporation, clear, dry nights speed it up. Some may mistake this for a leak, but consistent, gradual water loss—particularly after warm days followed by cool nights—is often just natural physics at work.

To minimize overnight evaporation, experts recommend using a pool cover. Not only does it trap heat and reduce chemical loss, but it can cut water evaporation by up to 90%. For pool owners, that means less refill hassle, lower heating costs, and more stable water chemistry.

So yes—water absolutely evaporates at night. And while you’re sleeping, your pool could be quietly losing gallons to the atmosphere, all thanks to the invisible pull of temperature and air flow.