Feb 22, 2011 at 7:57 pm #1269592
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 ("8×8"). A survey of the medical literature shows no evidence to support this claim.[Valtin 2002] In order to believe the 8×8 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 '8×8'?," 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.Feb 22, 2011 at 8:51 pm #1700278
@jjpermanLocale: Northern Rockies
Thank you! Thorough, concise and researched advice on a most important subject. Much appreciated.Feb 22, 2011 at 9:47 pm #1700293
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> Among backpackers on long through-hikes, it has a reputation for unreliability.
That relates mostly to the earliest models, which had some bugs.
My experience with later models has been very good.
CheersFeb 22, 2011 at 9:57 pm #1700300
Very interesting! I remember reading an article either here, or in the PCTA magazine, that came to the opposite conclusion regarding water on the top surface of lakes. If I am remembering correctly, the top few inches of water on lake surfaces get sufficient UV exposure to be somewhat disinfected. Thoughts?
Edited to Add: I used the Steripen Opti for about 1300 miles worth of hiking on the PCT last summer, and also found it to be reliable, easy to use, and lightweight considering the advantages. I previously had the regular Adventurer model with the electrode sensors, and found that to be very finicky, however.Feb 22, 2011 at 10:26 pm #1700309
Ben 2 WorldParticipant
@ben2worldLocale: So Cal
Ditto. I used my Steripen Adventurer regularly on a 7-month trip in 2009 and a 2-month trip last year without a hitch.Feb 23, 2011 at 12:47 am #1700329
@foundLocale: Sacramento, CA
> Among backpackers on long through-hikes, it has a reputation for unreliability.
That relates mostly to the earliest models, which had some bugs.
My experience with later models has been very good.
+1 they seem to be working well for the long distance hikers that i know. myself included.Feb 23, 2011 at 12:49 am #1700330
@ngatelLocale: Southern California
Like so many things in life, a lot of this varies by individual. I drink a lot less than many people, and pretty much have a cast iron stomach. My wife on the other hand needs to drink much more water and can get stomach ailments from all kinds of food in restaurants or at home.Feb 23, 2011 at 4:35 am #1700352
Since this is a cross-post from a research paper, I'm curious if that is a typo. It seems as if he just dropped the "unreliable" bomb, then left it hanging with no supporting evidence re: unreliability.
All previous citations were regarding bulk and finite lifespans, nothing regarding breaking. I used a newer Steripen exclusively on a 5 day trip to the BWCA last year. All went well…Feb 23, 2011 at 5:33 am #1700359
Steripen=backcountry bliss. Been using one for years. No issues.Feb 23, 2011 at 5:51 am #1700365
@er1kksenLocale: The Western Door
Fears of giardia may be exaggerated, but play it safe around beavers (major carriers of giardia). An instructor I had for some wilderness courses had a mechanical valve in his heart thanks to the little buggers: leading a trip several decades ago, not long after giving the kids he was leading a lecture on the necessity of carefully boiling any water source that may have been contaminated by beavers (this was the 70s), he soaked his bandanna in the water of a beaver pond to hang around his neck. This led to some hand-to-mouth contamination, which resulted in violent illness a couple weeks later when the incubation period had elapsed, which led to a session in the ICU where it was determined that giardia had somehow migrated into his bloodstream and wreaked havoc there, causing the damage that eventually required him to get a valve replaced. Crazy stuff.
That said, I tend to agree with the general points made. After all, if everything must be treated to sterility and we must drink a liter per hour of activity at all times, how the heck did we ever survive to the point where we have the luxury of being able to do so?Feb 23, 2011 at 6:20 am #1700380
@jamesdmarcoLocale: Finger Lakes
Yeah, they are pretty reliable these days. Last year was the first I fully trusted my health to one, though.
While I have had a few failures, these could always be traced to some sort of external fault:
1) Battery Power being drained away. (Especially with older models.)
2) Cold (Battery power is again the main culpret, some UV reduction from recent posts.) But, in very cold conditions, even with the batteries in my pocket, it has refused to turn on. Soo, there must be a feedback loop to the lamp itself. Now days, I just zip it into my cargo pants and this works for a pint of water, but it can cool off rapidly if you do not use it.
3) Dropping it. This is my main concern. I make a habit of walking away from streams and into the forst before treating the water. I HAVE dropped it a couple times, but, on loamy fabric soils, it doesn't really matter. So, this is highly recommended. I do not treat it over the rocks in a creek.
4) Potential for being fragile. This has turned out to be unfounded over the past years I have had the Adventuror. It seems immune to the shocks and vibration of backpacking.
Anyway, I would say that the research is somewhat dated.Feb 23, 2011 at 7:12 am #1700389
@retiredjerryLocale: Oregon and Washington
Great article, thanks
Nice that it has references to back up claims
I only carry one pint of water with me. Only recent time I've had a problem was a day hike in the summer – should have take two pints then.
I like that it says how to find good water. I only treat water about half the time.
I have heard that lake water is good because UV light from sun disinfects, but this article says the opposite, interesting.
I like that it says you don't have to boil water for so many minutes like the authorities tell you to do.
I've been using Adventurer Opti for a few trips. Once one of the batteries died. Maybe you need to carry a spare pair of batteries.
Most of my water is heated for cooking or coffee or whatever. I think based on this article I'll have my Platypus bottle be untreated water. I'll treat just the water I drink cold. Batteries will last longer.Feb 23, 2011 at 7:47 am #1700404
My guess, and it's only that, is that while exposure to sun (UV rays) will tend to sterilize the top layer of water in a lake, the water surface itself will catch any air born contaminates, while floating contaminates will be at the top, and surface tension will tend to keep things there.
The outflow of the lake, or the middle if you have very long arms (!), may have the most sterile water, if you follow the above good advice about going down an arm's length.Feb 23, 2011 at 11:12 am #1700482
In my normal stomping grounds, I sometimes take a swig of water directly from the middle of a lake if I'm really thirsty. Most of the Canadian Shield lakes are very deep, big, and pristine.
Sometime you'll run into a lot of tannin staining, but I think the rule of thumb about looking out for beaver huts and staying away from water inputs will keep you relatively out of harms way.Feb 23, 2011 at 11:52 am #1700500
Disagree with some of what that dude wrote about, including the urine color and other stuff.
Hydration Measurement and Monitoring
Water makes up approximately 63% of the total body mass in adults, 65% in children and 70% in infants. It is the medium of circulatory function, biochemical reaction, metabolism, substrate transport across cellular membranes, temperature regulation and numerous other physiological processes. As such, it is the most essential body nutrient, after oxygen.
Typical daily fluid intake and output for a healthy 70 kg (154 lb) person is about 2.4 liters (5.1 Pints). Humans can not reduce water losses from the body to less than about half this amount per day because water is involuntarily lost through the skin, respiration, faeces, and a minimum daily urine volume of about 0.4 liters. Sweating, governed by the body's need for temperature regulation, represents an additional loss that can be as much as 3.5 liters per hour during strenuous exercise. As a result, though human beings can survive for weeks without food, they die within days without water.
The sensation of thirst becomes apparent when water loss approaches 1%-2% of total body mass (approximately 3.0 lbs for a 150 lb person). It follows, therefore, that a person is already mildly dehydrated by the time they feel thirsty. As dehydration progresses, symptoms become increasingly severe and susceptibility to dehydration-related conditions, such as heat exhaustion, and heat stroke, escalate. Signs and symptoms of mild dehydration (2-4% loss of body mass) include the initial onset of thirst, dry mucous membranes, mild fatigue, loss of appetite, headaches, loss of concentration, irritability, decreased blood pressure (hypotension), and dizziness or fainting when standing up (due to orthostatic hypotension). Moderate dehydration (4-7% loss of body mass) may result in lethargy or extreme sleepiness, nausea, confusion, tingling in the limbs (paresthesia), heat cramps, seizures, fainting and significant decreases in aerobic power and endurance. With severe dehydration (8-10% loss of body mass), muscles may become spastic, skin may shrivel and wrinkle, vision may dim, urination may become painful, delirium may begin and recovery without assistance may be impossible. A body weight loss greater than 10-12% is usually fatal.Feb 23, 2011 at 12:05 pm #1700513
Good discussion going here, everyone.
So the American Journal of Physiology says this about concentration of solutes in urine (what makes it dark):
Dark Urine Means Dehydration:
Whether or not this statement is correct will depend on how dark the urine is, because the depth of color in urine will vary inversely with the urinary volume. Although the volume varies greatly among individuals, in our student laboratory (see above, under Other Data Since “8 × 8”) the mean value was 1,520 ml/24 h (Table 3), with a mean urine osmolality of 590 mosmol/kgH2O. Both values are those generally cited as being “normal,” namely, 1,500 ml/24 h and 600 mosmol/kgH2O, respectively (73, 92). At a urine osmolality ∼600 mosmol/kgH2O, the concentration of solutes in the urine is such that the urine has a moderately yellow color, which might be interpreted as “dark,” especially when contrasted against “pale yellow” or “clear,” which is specified in most of the lay literature (26). Yet, at the above-cited normal urinary volume and osmolality, the plasma osmolality will be well within the normal range and nowhere near the values of 300 mosmol/kgH2O and higher, which are seen in meaningful dehydration. Therefore, the warning that dark urine reflects dehydration is alarmist and false in most instances.
For sake of argument, that entire site is great for this topic.Feb 23, 2011 at 12:17 pm #1700525
I only ever boil my water to clean it, and sometimes I don't even do that at a few spots I know. I found a spring in the middle of the woods that comes right out of the side of a hill. It is a real delight and feeling of freedom drinking directly from the spring itself.
Then again, I also live in Sweden, which has very clean water in general. When I used to live in the USA, I did a lot of AT hikes (mostly in PA) and used iodine pills. I actually didn't mind the taste at all.
I think the biggest thing with water is where you are at down to the smallest detail. Even when I drink raw, wild water, it is after I have looked around to make sure no dead animals are in it, that it is running water, that it is clear, etc. When I use lake water, I always boil it, even here in Sweden.Feb 23, 2011 at 12:47 pm #1700546
First some likes. I like the citations of sources. There is too much repetition of opinion and misleading anecdotal information out there.
One of the myths accurately debunked is the 8×8-glasses-per-day-no-matter-what advice which, apparently, was made up out of thin air and then repeated thousands of times.
I think there is some merit in the "don't wait until you're thirsty," in extreme conditions. I fought wildfire for a living and when I started drinking water BEFORE I was thirsty I got way less dehydration headaches. Took me years to learn that. To me it's sort of like "put on your jacket before you get cold, take it off before you get hot."
"Backpackers get sick from Giardia in the water" is definitely not a myth. Now, I have absolutely no doubt that many sicknesses are inaccurately blamed on Giardia. I have no doubt that even when accurately diagnosed the source might not have been drinking water, as believed. But to say that backpackers cannot get Giardia from backcountry drinking water simply defies logic.
Robert L. Rockwell, PhD wrote one often cited paper "debunking the Giardia myth." http://pweb.jps.net/~prichins/giardia.htm Some quotes:
"(Giardia) Cysts were found at only 18 (43 percent) of the high-use sites and at 5 (19 percent) of the low-use sites…"
"…But be careful with statistics: Animal droppings containing 100,000 Giardia cysts deposited at the edge of a 10 million liter lake may be an average of only 0.01 per liter for the lake as a whole, but in the immediate vicinity of the deposit, the concentration can be much higher."
Based on that alone, common sense tells me that it's possible to get Giardia from drinking water.
Dr. Rockwell accurately points out that even if you contract Giardia you may not get sick, and you may recover without treatment if you do, etc. But I think he has relied far too much on a limited study of Sierra water and in part on anecdotal evidence, the same type of evidence that "Giardia fear-mongers" are accused of using.
Some more quotes from the EPA: http://water.epa.gov/action/advisories/drinking/upload/2009_02_03_criteria_humanhealth_microbial_giardiafs.pdf
"Since 1971, Giardia has been the most commonly identified pathogen in waterborne outbreaks reported in the United States…Outbreak statistics emphasize the need for filtration of surface water, optimization of the filtration process, frequent monitoring of treatment effectiveness, and better protection and treatment for ground water…"
"Giardia can be an important cause of endemic and epidemic waterborne illness. In the United States, increased risks have been found in populations where surface water sources are not filtered, persons who use shallow well water systems, persons who drink contaminated water while picnicking, camping, and hiking…"
Last summer I hiked the PCT. Despite having been diagnosed with Giardia twice before in my life, I had read Dr. Rockwell's paper and believed his study over my own experience. For the first time in over 20 years I didn't treat my drinking water most of the time. Instead I was the most conscientious I've ever been on hand sanitation. I got sick north of Mammoth Lakes. Many thru-hikers have gotten Giardia in that area. A physician diagnosed Giardia in my case. He says he treats it a lot and like most doctors doesn't report it. When I told him about the study, he laughed. He says not enough sources of water were tested in that study to make an accurate evaluation of risk, and regardless, lots of hikers come to him with Giardia after visiting the backcountry. He himself treats all his water.
Many people that I know have been drinking backcountry water for years and have never gotten sick. Lots more have done so and have subsequently been diagnosed by doctors with Giardia. I don't know what the numbers are to the risk, but there is some risk. Obviously, I've gone back to treating my water.Feb 23, 2011 at 12:56 pm #1700556
"Typical concentrations of Giardia cysts in the Sierra are ten times less than those found in San Francisco city water."
Doesn't SF come come for Hetch Hetchy? Then where is the Giardia coming from?Feb 23, 2011 at 1:02 pm #1700561
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
> The sensation of thirst becomes apparent when water loss approaches 1%-2% of total
> body mass (approximately 3.0 lbs for a 150 lb person). It follows, therefore, that a person
> is already mildly dehydrated by the time they feel thirsty.
There is a complete lack of logic here. Actually, the statement is just false. Yes, you get thirsty at the levels indicated, but medical dehydration does not start until you have lost about twice that much weight/water. The author is just ignoring the standard medical definition.
> Signs and symptoms of mild dehydration (2-4% loss of body mass) include the initial
> onset of thirst, dry mucous membranes, mild fatigue,
Blimey, the author must be a complete couch potato or woos! How many of us have experienced that when walking? :-)
Even so, a famous US military study found that soldiers marched to the point of dehydration collapse recovered 100% within about 15 minutes after drinking. Some people just have an irrational fear of ever being thirsty.
CheersFeb 23, 2011 at 1:16 pm #1700579
@b-g-2-2Locale: Silicon Valley
Once, many years ago, I was in military training in a warm place. It was our day to go out on a 15-mile road march with full gear. We were told to start with one full water bottle, and that there would be water available at the mid-point and at the end. Some got a little dry during the first half, and they did not grab up the available water at the mid-point, so by the time they got to the last few miles, they were suffering. One guy collapsed from heat exhaustion, and once he rested in the shade with a cool drink, he recovered quickly. One guy collapsed from heat stroke, so he was already so far dehydrated that his body temperature was shooting up. He did not recover well and suffered permanent brain damage.
I prefer to avoid being in those categories.
–B.G.–Feb 23, 2011 at 1:53 pm #1700603
@greg23Locale: ColoradoFeb 23, 2011 at 2:11 pm #1700624
@halfturboLocale: Northernish California
"Doesn't SF come come for Hetch Hetchy? Then where is the Giardia coming from?"
Agreed, it's perhaps a made-up "statistic." SF's most recent (2009) water quality report is here.
Key value–0.01-0.05 cysts per liter in the delivered water. If that implies typical Sierra water is 0.001-0.005 cysts per liter I'd love to know based on what. For the record, SF's water quality is among the best–we should all be so lucky. The author could have picked a better point of comparison.
FWIW it's common for contamination to enter a water supply through the transportation and distribution system. If SF has a contamination spike in their century-old system they probably first look at the piping network and for cross-connections and backflow issues. Maybe "herd of dead moose in Hetch Hetchy" comes second.
p.s. I still treat Sierra water unless I've reconnoitered the source to my satisfaction.Feb 23, 2011 at 2:20 pm #1700632
@b-g-2-2Locale: Silicon Valley
First of all, there are no dead moose in Hetch Hetchy. There are no live moose, either. Moose do not live anywhere around Hetch Hetchy.
Water leaves the Hetch Hetchy Reservoir and flows downhill. It is taken at some of the intake points and piped into large closed aqueducts where it flows across the Central Valley. Eventually, it is dumped into Crystal Springs Reservoir where it is open to any natural contamination you could imagine. Later, it enters the San Francisco public water system.
I live in a municipality that gets water from the aqueduct before it ever gets to Crystal Springs Reservoir, so the water is possibly cleaner than in San Francisco.
–B.G.–Feb 23, 2011 at 2:32 pm #1700643
@bcrowellLocale: Southern California
I'm the author of the article. Glad to see that some people are finding it helpful!
'Agreed, it's perhaps a made-up "statistic." SF's most recent (2009) water quality report is here.
Key value–0.01-0.05 cysts per liter in the delivered water. If that implies typical Sierra water is 0.001-0.005 cysts per liter I'd love to know based on what. For the record, SF's water quality is among the best–we should all be so lucky. The author could have picked a better point of comparison.'
The reference for the statistic is given in the article: [Rockwell 2002]. He gives 0.12 cysts/liter as the typical level in SF water in 2002, which is more than double the high end of the range given in the 2009 sfwater.org data, so maybe SF has improved their filtering between 2002 and 2009. Even so, the typical concentrations in Sierra water are indeed very low, often undetectably low or at the level of a few cysts per thousand liters. Rockwell says that out of 69 sites in the Sierra, 67 had concentrations of giardia lower than 0.03 cysts/liter. I'll revise the article so that it's not using the out of date SF numbers.
The statement about the unreliability of steripens is based purely on anecdotal evidence. I'll revise article to say so, and to say that more recent models may be more reliable.
You must be logged in to reply to this topic.