Here's some food (or, water) for thought. I've been waiting to post something worth while after becoming a member, so hopefully it offers some insight. Enjoy!
Original article can be found at: http://www.lightandmatter.com/article/hiking_water.html
This article discusses some of the popular mythology surrounding hydration and water contamination, from the point of view of hikers and backpackers.
Myths about hydration
Our popular culture has picked up some pervasive myths recently that wildly exaggerate the dangers of dehydration. Among people with sedentary lifestyles, there is a widespread belief that one should drink at least eight 8-ounce glasses of water per day ("8x8"). A survey of the medical literature shows no evidence to support this claim.[Valtin 2002] In order to believe the 8x8 myth, you would have to believe that your body was always lying to you about how much water you needed, hence the subsidiary myth that "thirst is too late," i.e., that you need to drink when you're not thirsty, because by the time you're thirsty, you're already dehydrated. In fact, thirst is one of your body's most powerful instincts. Medically, dehydration is defined as a 5% increase in the concentration of solutes in your blood. (Often this can be more conveniently detected based on short-term weight loss.) Thirst sets in at about 2%, so you'll always feel strong thirst setting in long before you're dehydrated. It is also not true that dark urine indicates dehydration.
Because of the "thirst is too late" myth, many hikers carry huge amounts of water -- sometimes as much as several liters, often in a hydration pack. Hydration packs are heavy (about 9 oz for a large one), and water is very heavy. Three liters of water in a 9-oz hydration pack adds up to 7.2 pounds of extra pack weight, which is a huge amount of weight to be carrying based on a mistaken belief. In moderate summer weather in the Sierra, on a trail where streams are no more than a few miles apart, there is theoretically no reason to carry any water from point to point. In reality, you'll want to carry some, for a variety of reasons. You may be treating your water with tablets that take a certain amount of time to work; or camping at some distance from over-impacted areas near lakes and streams; or in late season you may be uncertain whether the creeks and streams on your map are actually running. Nevertheless, one liter per person is usually plenty of water to carry under these conditions, and you can carry that in a couple of lightweight plastic water bottles of the type that bottled water is sold in. This adds up to 2.3 immediately after refilling both bottles.
Proponents of the dehydration myth commonly claim that alcoholic and caffeinated drinks "don't count," because alcohol and caffeine dehydrate you. In fact, beer consumed in moderation has a hydrating, rather than a dehydrating, effect,[Valtin 2002] and laboratory studies have shown that caffeinated soda is just as hydrating as water, i.e., the diuretic effect of the caffeine is too small to measure.[Grandjean 2000] Even in the case of coffee, which has much higher concentrations of caffeine than soda, studies going back as far as 1928 have shown that the diuretic effect vanishes for people whose bodies have learned to tolerate the caffeine.[Eddy 1928]
Myths about contaminated water
Backpacking involves a change in your diet and daily routine, which can disrupt bowel function. Many backpackers get constipated,[Mueser 1997, p. 101] while others report "backpacker's diarrhea." Diarrhea hits about 10-20% of backpackers on short trips, more than 50% on long through-hikes.[Zell 1993,Mueser 1997]
Myth: Backpackers get sick from Giardia in the water.
Many people who experience diarrhea while backpacking automatically attribute the problem to Giardia, which is the most popularly known microorganism that can contaminate backcountry water supplies. Unless these people are doing long through-hikes, it is almost certain that their illness was not caused by wilderness-acquired Giardia, which has a 1-3 week incubation time.
Giardia is a big problem in daycare centers and public swimming pools, but recent data show that its prevalence in the backcountry has been wildly exaggerated. Typical concentrations of Giardia cysts in the Sierra are ten times less than those found in San Francisco city water.[Rockwell 2002] Similarly low concentrations have been found in other areas of the U.S.[Jaret 2003] Very few people who believe they contracted giardiasis from backcountry water ever get tested for it, and of those who get tested, most have negative results. Even when the results are negative, doctors often prescribe medication as a prophylactic. When the results are positive, the long incubation period makes it more likely that the hiker picked up the bug somewhere else, perhaps by changing a diaper or eating at a salad bar. A meta-analysis of the literature in 2000 concluded that "the evidence for an association between drinking backcountry water and acquiring giardiasis is minimal."[Welch 2000]
Wash your hands!
When people do actually contract backpacker's diarrhea from exposure during a hiking trip, by far the most common reason is hand-to-mouth contamination.[Welch 1995] Your gut contains so many bacteria that if your body was a democracy, the germs would outvote the human cells by a large margin. You've developed tolerance for your own gut flora, but not for other people's. If your hiking partner doesn't wash his/her hands properly after defecating, then you can ingest their bugs through shared food, food containers, or pots and pans. Hiking groups are extremely prone to contaminating each other with organisms such as E. coli and shigella. To guard against this, don't lower your standards of bathroom hygiene while hiking. (Don't rinse your hands in a stream, because the soap is environmentally damaging. Do your hand-washing in the same area where you do your defecating, i.e., as far as possible from lakes and streams.) If possible, avoid using cooking pots -- either by by going no-cook or by using foods that are cooked by pouring hot water into an individual-use bag. If you must use pots, wash them thoroughly after each use, and consider using a one-pot system, in which each person eats only from his/her own pot.
You can treat your drinking water without incurring a lot of extra weight, expense, or inconvenience, so you might as well do it. Tablets will save you about 5 ounces of pack weight compared to most filtering systems, and are less time consuming to use. But don't let water treatment distract you from the real issue, which is hand-to-mouth contamination; a 1997 study found that among a large sample Appalachian Trail through-hikers, a majority of whom experienced diarrhea at least once, there was no correlation between the use of water treatment and the risk of diarrhea.[Mueser 1997]
Water treatment works differently for bacteria and viruses than for cysts of the protozoa Giardia and Cryptosporidium. Iodine doesn't work well against protozoans, but filters do, and chlorine dioxide tablets are effective if you wait long enough (up to four hours for very cold water). One low-weight, low-cost system is to use iodine to kill bacteria and viruses, plus a small 2-oz filter that fits on the mouth of the bottle to get rid of protozoa cysts. But remember, getting sick from Giardia in your water is little more than an urban folktale, and field surveys show that concentrations of Cryptosporidium are also much too low to be a health threat.[Jaret 2003] Since the techniques that work against protozoans all have drawbacks (inconvenience or higher cost), it may not be worth worrying about them. A survey of Appalachian Trail through-hikers showed that filters were one of the most failure-prone pieces of equipment, leading to comments such as "not worth the money or the effort."[Mueser 1997, p. 95]
The Steripen UV system is effective against all microbes, including viruses and protozoa cysts. It's worse than chemical treatments in terms of bulk and weight (3.6 oz with batteries), but it works in only a couple of minutes. The batteries will last for more days than you can hike without resupplying. There is an initial investment of about $90, and the lamp has a finite lifetime. It's definitely worth considering for day-hikes, for traveling in the third world, or for hikes in areas where protozoan-contaminated water is a big enough risk to be worth worrying about. Among backpackers on long through-hikes, it has a reputation for unreliability.
Myth: When you treat water by boiling, you have to boil for a certain number of minutes.
If you're boiling water for use in cooking, then the water is already pasteurized before it reaches the boiling point. It is not necessary to use filtering or chemical treatment, and iodine treatment may even cause foods like instant mashed potatoes to turn a funny color. It is not necessary to boil for a certain amount of time in order to kill microorganisms. Protozoa cysts are killed rapidly at about 55 C (131 F). Common bacteria and viruses such as E. coli, Shigella, and Hepatitis A are all killed rapidly at temperatures at or below 65 C (149 F). Even raw milk (which can be swarming with microbes compared to backcountry water) is normally pasteurized for only 15 seconds at temperatures of no more than 72 C (161 F), based on standards designed to kill the most heat-resistant disease-causing bacteria.[USDA 2004] Although the boiling point is depressed at higher altitudes, even at the 26,000-foot elevation of Everest base camp it's 72 C (161 F), which is high enough for complete pasteurization.
Picking a source
It is worthwhile to take your water from the cleanest possible place. The best source is a fast-running stream that is not below any trail or close to any area where you see droppings from livestock. (Calves, in particular, excrete a huge amount of cryptosporidium compared to wild animals or adult cows. Cattle are also prolific sources of E. coli.) Inlets of lakes are better than outlets, and outlets are better than the calm water of the lake itself. If you must collect calm water from a lake, avoid the surface layer by covering the mouth of the bottle and plunging it in to arm's depth before letting any water in. Avoid areas that seem like likely swimming spots for humans, or areas around beaver dams (beavers tend to carry a lot of giardia).
If you are forced to drink from a source that isn't running rapidly, be aware that blue-green algae can produce toxins that can make you sick. Treatment will not get rid of the toxins. Even after an algae bloom has died off, the toxins can remain in the water if it's stagnant. The only way to avoid this problem is to plan your hikes so that you never have to drink from such sources.
Some hikers add drink mixes to some of their water. This adds variety to the monotonous diet of a long hike, and for people who can taste iodine, the mix masksthe taste. Mixes can be either zero-calorie (e.g., Crystal Light) or sweetened with sugar (e.g., Kool-Aid). If you use the ones sweetened with sugar, be scrupulous about cleaning the threads of your water bottles, because otherwise you may risk dysentery.[Mueser 1997, p. 100] If you're using chemical treatment, wait until it's complete before adding the mix.
Eddy 1928 - Eddy NB, Downs AW. Tolerance and cross-tolerance in the human subject to the diuretic effect of caffeine, theobromine and theophylline. J Pharmacol Exp Ther. 1928;33:167-174.
Grandjean 2000 - Grandjean et al., "The Effect of Caffeinated, Non-Caffeinated, Caloric and Non-Caloric Beverages on Hydration," Journal of the American College of Nutrition, Vol. 19, No. 5, 591-600 (2000) http://www.jacn.org/cgi/content/full/19/5/591
Jaret 2003 - Peter Jaret, "What's In the Water?," Backpacker, Dec. 2003, p. 45.
Mueser 1997 - Roland Mueser, Long-Distance Hiking: Lessons from the Appalachian Trail, International Marine/Ragged Mountain Press, 1st edition, 1997, p. 96
Rockwell 2002 - Robert L. Rockwell, Sierra Nature Notes, Volume 2, January 2002, http://web.archive.org/web/20051026030831/www.yosemite.org/naturenotes/Giardia.htm
USDA 2004 - National Advisory Committee on Microbiological Criteria for Foods: Requisite Scientific Parameters for Establishing the Equivalence of Aalternative Methods of Pasteurization, USDA , 2004
Valtin 2002 - Heinz Valtin, "'Drink at least eight glasses of water a day.' Really? Is there scientific evidence for '8x8'?," Am J Physiol Regul Integr Comp Physiol 283: R993-R1004, 2002. http://ajpregu.physiology.org/cgi/content/full/283/5/R993
Welch 1995 - Thomas R. Welch and Timothy P. Welch, "Giardiasis as a threat to backpackers in the United States: a survey of state health departments," Wilderness and Environmental Medicine, 6 (1995) 162, http://www.wemjournal.org/article/S1080-6032%2895%2971046-8/abstract
Welch 2000 - Welch, T.P. "Risk of giardiasis from consumption of wilderness water in North America: a systematic review of epidemiologic data," Int J Infect Dis. 2000;4:103100, http://download.journals.elsevierhealth.com/pdfs/journals/1201-9712/PIIS1201971200901024.pdf?refuid=S1080-6032(04)70498-6&refissn=1080-6032&mis=.pdf
Zell 1993 - S.C. Zell and S.K. Sorenson, "Cyst acquisition rate for Giardia lamblia in backcountry travelers to Desolation Wilderness, Lake Tahoe," Wilderness and Environmental Medicine 4 (1993) 147, http://www.journals.elsevierhealth.com/periodicals/jwm/article/S0953-9859%2893%2971172-9/abstract
Edited by Roger Caffin to improve heading layout.