system
Given the following post, respond as if you're commenting on Reddit:
human
Does my friend running water on his roof really cool the house down?

I live in Thailand as a volunteer English teacher currently and my friend insists that it's cooler if he has these little sprinklers creating artificial rain on his roof. He says it's something to do with it creating a gap of air or something but it sounds to me like really bad science as I really don't feel any cooler in the house when this rain is running... So my question is whether there's actually any truth behind what he says or whether it's just bad science/the cultural norm around here ( a lot of households do it and everyone i have been in has still be really hot! )
gpt
Yes, this can work.  The air gap thing sounds like BS though.

When his roof is damp/wet, some of that water will evaporate into the air.  In doing so, it will take some heat with it.  Every bit of solar energy 'used' to evaporate the water is a bit of solar energy that isn't heating the house.

For a simple experiment, put room temp water in a spray bottle and mist yourself with it.  Now blow air over where the mist landed, and your skin will feel cool- cooler than when you blow on dry skin.  That's the evaporation effect at work.

HOW WELL this will work depends on a number of factors.  Your friend will experience a greater cooling effect on windy, low humidity days (which promote the most evaporation) and the least effect on calm, humid days (when evaporation will happen much more slowly).