Here is a comprehensive page on preventing Heat Illness:
(Drinking water alone without taking in electrolytes can be dangerous!)
Heat-Related Illnesses – Prevention
The following tips may help prevent a heat-related illness. Be aware of the symptoms of heat-related illnesses and the warning signs of dehydration.
Practice heat safety measures when you are physically active in hot weather. This is especially important for outdoor workers and military personnel. Avoid strenuous activity in hot, humid weather or during the hottest part of the day (between 10 a.m. and 4 p.m.). Use caution during your physical activity in the heat if you have health risks.
Drink plenty of water before, during, and after you are active. This is very important when it’s hot out and when you do intense exercise. Fluids such as rehydration drinks, juices, or water help replace lost fluids, especially if you sweat a lot.
Drink on schedule. Two hours before exercising, drink 24 fl oz (750 mL) of fluid. Drink 16 fl oz (500 mL) of fluid 15 minutes before exercising. Continue drinking 8 fl oz (250 mL) of fluid every 15 minutes while exercising.
Drink rehydration drinks, which are absorbed as quickly as water but also replace sugar, sodium, and other nutrients. Eat fruits and vegetables to replace nutrients.
Check your urine. Urine should be clear to pale yellow, and there should be a large amount if you are drinking adequately. You should urinate every 2 to 4 hours during an activity when you are staying properly hydrated. If your urine output decreases, drink more fluids.
Do not spend much time in the sun. If possible, exercise or work outside during the cooler times of the day. Wear lightweight, light-colored, loose-fitting clothing in hot weather, so your skin can cool through evaporation. Wear a wide-brimmed hat or use an umbrella for shade.
Stay cool as much as possible. Take frequent breaks in the shade, by a fan, or in air-conditioning. Cool your skin by spraying water over your body. Take a cool bath or shower 1 or 2 times a day in hot weather.
If you have to stand for any length of time in a hot environment, flex your leg muscles often while standing. This prevents blood from pooling in your lower legs, which can lead to fainting. To prevent swelling (heat edema), wear support hose to stimulate circulation while standing for long periods of time.
Do not drink caffeine or alcohol. They increase blood flow to the skin and increase your risk of dehydration.
Staying physically fit can help you acclimate a hot environment. Before you travel to or work in a hotter environment, use gradual physical conditioning. This takes about 8 to 14 days for adults. Children require 10 to 14 days for their bodies to acclimate to the heat. If you travel to a hot environment and are not accustomed to the heat, cut your usual outside physical activities in half for the first 4 to 5 days. Gradually increase your activities after your body adjusts to the heat and level of activity.
Be aware that when the outdoor humidity is greater than 75%, the body’s ability to lose heat by sweating is decreased. Other ways of keeping cool need to be used. The National Weather Service lists a heat index each day in the newspaper to alert people of the risk for a heat-related illness in relation to the air temperature and humidity of that day. Direct exposure to the sun can increase the risk of a heat-related illness on days when the heat index is high.
People who have had heatstroke in the past may be more sensitive to the effects of heat in the first few months following the illness, but they do not have long-term problems.