Even if you do not plan to do any hiking, you should wear a hat, carry one quart of water with you at all times, wear sunscreen, and wear sunglasses. If you start to feel nauseated, weak, tired, or feel like you cannot cool down, you are showing signs of heat stress. Listen to your body and get into some shade. Medical emergencies can be reported to 911 or by using any of the emergency phones dispersed throughout the park and on selected hiking trails. Heat plus dehydration can be life threatening.
High altitude coupled by direct sunlight accelerates dehydration.
While at Grand Canyon National Park you should try to drink one gallon of clear, un-carbonated liquids a day. Do not wait until you are thirsty to have a drink. If you wait to the point you are craving a drink, you have waited too long. Carry at least one quart of water with you at all times. If you plan to hike, you should carry at least one gallon of water with you.