A pool cover stops most of it.

Yes, a cover. It’s the single most effective way to cut evaporation on a hot day—by 90% or more. Everything else is a distant second.

The physics is simple: hot, dry air and wind wick water away from the surface. A cover physically blocks that contact. Solar blankets (the clear bubble-wrap style) also passively heat the water during the day, which is a nice bonus if you want warmer swimming.

Liquid solar covers (a chemical that spreads a thin invisible layer on the surface) work okay in calm conditions but break apart in any breeze. Windbreaks—fences, hedges, or shade sails—help more than you’d expect, especially if your pool sits in an exposed spot. Shade from trees or a structure also reduces direct sun heating, which slows evaporation.

But honestly, the cover is the thing. Throw it on when you’re not swimming. Your water bill will thank you.