With the arrival of the hot season, it’s a good time to reevaluate your individual water supply you will be carrying on the trail. As temperatures increase, so do hydration requirements. A single water bottle or small hydration pack that sufficed for an all-day hike during the winter won’t be nearly enough when you are sweating in the desert summer sun. In Tucson, all experienced desert hikers and backpackers carry sufficient water to reach their destination or refilling station, plus additional water as a reserve in case of higher-than-expected temperatures, off-trail excursions, or a trail route that takes longer than anticipated. If you’re drinking 100% of your water on your hikes, you’re not carrying enough.
In the lower Sonoran Desert, natural water sources can be very scarce except immediately after a rain, which means that more water has to be carried than would be required in other outdoor environments. In hot weather (over 100° F or 38° C), water consumption goes up dramatically. According to one U.S. Army study, the average person exercising in full sun can expect a fluid loss of two quarts per hour (three gallons in six hours). A loss of only 2.5 percent of body weight (two quarts) from the body can impair thinking, increase one’s heart rate, and reduce overall endurance, while a loss of eleven percent of body weight (just over two gallons, or eight liters) can be fatal.
Drinking more water is the obvious solution, but there is a problem in that the human body can only process approximately 1 liter (34 ounces) of water per hour in extreme heat. Exceeding this rate can lead to hyponatremia (acute water intoxication), a life-threatening condition caused by a chemical imbalance in the body’s electrolyte levels.
To stay safe, begin increasing your water intake during the 24 hours before your trip commences. Some people don’t drink any extra water before starting out, and this is a mistake, because it robs you of the opportunity to store water where it will do the most good – inside your body. It’s always more efficient to carry water in your bloodstream and body tissues than on your back. So drink slowly but steadily and regularly, even if you don’t feel thirsty, until you feel completely saturated with fluid. Eat light, hydrating foods such as melons and other fruits, while avoiding coffee, tea, or other diuretic beverages that tend to remove water from your system. To avoid excessive dilution of sodium chloride (salt) and other electrolytes that could cause hyponatremia, eat balanced meals that include whole grains, dark leafy greens, and fresh fruits with adequate salt. If you are new to hot weather hiking, you may want to increase your sodium levels a bit. Start out early when temperatures are cooler, and plan for more rest and water breaks than normal.
Once on the trail, your primary fluid intake should be water. A six-hour trek in hot temperatures can result in fluid loss similar to that experienced by athletes competing in strenuous competition. Depending upon the individual, this might require two gallons of water or more. For hikes exceeding two hours, alternating water breaks with a sports drink containing electrolytes is also a good idea. The International Marathon Medical Directors’ Association (IMMDA) recommends that athletes participating in strenuous exercise also use a sports drink if the event lasts more than 30 minutes. The sports drink’s added electrolyte and carbohydrate content will speed up the absorption of fluids and keep the body functioning efficiently.
Because of the impermanent nature of most natural desert water sources, hikers must not rely on these as refilling stations. Contact local authorities and/or landowners ahead of your trip to make certain that wells, springs, tanks, water taps, or other water sources will be available when needed, and never forget to carry some means of water purification or filtration. When you reach the next refilling point, take a long rest break and/or consider camping for the night. You will need extra time to rehydrate and recover from the added stress imposed on your body.