As you sweat during hot-weather exercise, the body’s temperature inches up, and heatstroke can result. Douglas Casa, of the Korey Stringer Institute, explains the best way to stay safely hydrated during summer activity — and why too much water can be a bad thing too.

In the SciFri Snack: Ready for the next heat wave? Douglas Casa tells us that to weather the weather, make sure you stay hydrated — the more water you lose, the hotter you’ll get. Hear more — and join the conversation — on SoundCloud.