How do you stay cool in a heatwave?

Stay hydrated. Water is essential for keeping you cool during hot weather. Water keeps your body cool and should be drunk even if you don't feel thirsty. It's okay to also drink commercial waters (such as Vitamin Water) or sports drinks such as Powerade or Gatorade but they're usually not necessary unless you're deliberately replenishing lost vitamins/electrolytes following a sporting activity.