A typical adult loses about one to two liters of fluid per hour working or exercising outdoors in the heat. Even easy activities like gardening mean losing a gallon of fluid in within a couple of hours when it’s scorching out.

That’s why experts recommend drinking copious amounts of liquid when the mercury soars, whether or not you feel thirsty. For people who are out in the heat, that means consuming about a glass of water every 10 minutes, said Harvey Meislin, director of the Arizona Emergency Medicine Research Center at the University of Arizona College of Medicine in Tuscon.

Studies show that humans have notoriously poor thirst sensation, said Kevin Kregel, a physiologist at the University of Iowa in Iowa City.

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