Do not just stay hydrated! ALSO: Avoid caffeine and alcohol. Wear light colored, loose fitting clothing. Wear a hat and use sunscreen. Avoid being outside in the hottest part of the day. If you don't have a/c, go to a heat relief shelter, mall, library. Don't bake. Don't roast. Choose stovetop meals

Generally avoid heavy meals. And last, but far from least, hyponatremia is a thing. Hyponatremia happens when you sweat a lot, replace the lost fluids, but don't replace the lost salt. During a heatwave, you need to increase your sodium intake. You can do this with sports drinks, salt tablets...

Also try to prevent solar gain in your house — blinds down etc during the sunny part of the day. And if you have some air conditioning but it’s struggling, make sure all your windows are locked down tight so the cool air isn’t escaping.