How much water do you need in the desert, on a hot summer day? Let's take a look.
But first, the brief article in today's Albuquerque Journal that inspired me to write this blog entry. (As is obvious from many other entries, I try to turn each hiking tragedy or near-tragedy into a teachable moment.) The article reads, in its entirety:
"U.S. Border Patrol agents rescued a 71-year-old man who went missing while hiking Monday in Indian Wells Canyon, east of Alamogordo.
"Border Patrol agents found the man under a bush, dehydrated and unable to walk, after an hour-and-a-half search, according to a news release from the agency.
"The U.S. Border Patrol Search, Trauma and Rescue Team sent a paramedic to treat the man on the scene and agents carried him to [an] area where a CPB helicopter could land. He was airlifted to Las Cruces for medical treatment.
"Authorities did not release the hiker's name."
In Alamogordo, the high temperature that day was 100 degrees F (38 C). Now let's take a look at a chart published by the U.S. Army. I'll list the publication at the end of this blog.
This rough guide suggest that in 90 degree weather, someone doing an easy hike (2,500 Kcal/day) should drink 8 quarts (7.6 liters) of water a day. It was 10 degrees warmer than that last Monday, so this hiker needed to drink more than two gallons over the course of the day. Otherwise, dehydration was inevitable. The incident reminds me of something I was told almost five decades ago: "Ration sweat, not water."
A couple more comments before I go.
First, hikers should be aware that it's possible to drink too much water, leading to hyponatremia, which can cause symptoms as severe as seizures, coma, and (rarely) death. This far less common concern is mentioned in the report I cite below.
Second, you may wonder how long it takes to rehydrate orally after moderate dehydration—that is, fixing the problem by drinking water. The answer, I've read, is about 45 minutes. In other words, when you suddenly realize that you're seriously dehydrated, drinking water isn't an instant cure. Instead, prevention is the way to deal with dehydration. On a hot day, make yourself drink water before you feel the effects.
Montain, Scott J., and Matthew Ely, 2010, Water Requirements and Soldier Hydration. Borden Institute, Fort Sam Houston, Texas. Link