Water needs - how much do you need?

It is 'well known' that you can go for many days without food and survive easily, but that you die in just a day or two without water. Fair enough: adequate clean water matters.

Water needs

It is 'well known' that you can go for many days without food and survive easily, but that you die in just a day or two without water. Fair enough: adequate clean water matters. However, this statement rather begs the question of:

How much water should you drink?

The short answer is a lot less than many of the self-styled 'experts' have claimed. A recent editorial in the British Medical Journal1 suggests the the current dictum that you should 'drink the maximal amount that can be tolerated' is horribly wrong and leads to hyponatraemia2. To quote: 'To date at least seven fatalities and more than 250 cases of this condition have been described in the medical literature.' The editorial goes on to suggest that 'In particular, exercisers must be warned that the overconsumption of fluid (either water or sports drinks) before, during, or after exercise is unnecessary and can have a potentially fatal outcome. Perhaps the best advice is that drinking according to the personal dictates of thirst seems to be safe and effective.' Apparently marathon runners have been trying to drink over 1 litre per hour, possibly over 1.5 litres, and up to 15 litres in a day, as a result of the drinking craze.

I was recently contacted by someone who ended up in hospital for two days as a result of hyponatraemia. After that he was still in care for another two days. Fortunately, he survived.

It seems good for a few hours around a campfire, or a few weeks around a news group. It is worth noting that the 'drink all you can' craze didn't exist before 1970, and we all managed quite nicely on the opposite regime. The craze has all the hallmarks of a good urban myth. For what it is worth, the FAQ maintainer and his wife typically take a 2 litre water bottle for the day (except in summer) and return with some left over. Granted, we may drink less than the average. In summer we usually take 3 litres. Novices are advised to allow a little more for themselves. It also happens that most walkers keep a water bottle near their sleeping bag in case they want a drink in the night. This happens more in the bush because your body is still 'rebalancing' itself after you have initially gone to sleep. That's fine, just take a few sips when you need it.

This has two implications for bushwalkers. The first is that the current craze for a 'hydration bladder' with a hose over your shoulder and nipple to suck on is just that: a bit of a craze, principally designed to transfer dollars from your pocket to that of the manufacturers and vendors. You simply do not need to drink that much, that often. The second is that most of the 'sports drinks' are useless at best, (usually taste awful) and are possibly dangerous at the worst. Discussion following the editorial included the following quote3

'Current sports drinks have low sodium concentration relative to sweat losses at maximum sweat gland function. Thus, it may be safer to increase the salt content of sports drinks to protect athletes performing under high heat rather than discouraging adequate replacement of losses. An added benefit would be that less serious athletes performing under lower ambient heat would not over-consume beverages with a higher electrolyte content. Normally hydrated individuals would find the brackish taste of more salty drinks less palatable. Such an idea obviously works against the thrust of the beverage industry that seek to cajole us all to drink as much as possible of any fluid they produce' [His words, my emphasis - RNC].


Water for cooking

Perhaps worth considering as well is the amount of water you need for the evening meal. This can be relevant when considering a 'high camp' where water is not available. Such high camps can be wonderful: dawn on top of a mountain is rather special. But you will need to carry water to the high camp, and water is heavy. How much should you allow?

In the hope of providing a starting point for experiment, I will quote my own experiences. I have successfully managed high camps for two people in cool weather on two 1.25 L PET bottles plus a smaller 0.5 L PET bottle, filled at lunchtime. We take a good drink during lunch of course, and expect to reach water for morning tea the next day. Note that it assumes maybe 500 metres of climbing; walking on the flat would need far less water. The water carried is used thus:

Drinks while climbing 2 * 150 mL 300 mL
Hand wash before cooking 100 mL 100 mL
Instant Noodle soup 2 * 250 mL 500 mL
Freeze-dry stew 500 mL 500 mL
Rice or Noodles 250 mL 250 mL
Cocoa 2 * 250 mL 500 mL
Washing up 150 mL 150 mL
Drinks in night 2 * 100 mL 200 mL
Breakfast 250 mL 250 mL
Total   2750 mL

This is dining in reasonable style but uses less than the 3 litres carried, which means we have a small safety margin as well. Novices are advised to carry a little more rather than take big risks. In hot weather - the Australian summer, we take an extra 1.25 L PET bottle. On the other hand, we have survived on rather less than one 1.25 L PET bottle on one occasion when things did not go quite as planned (there was a 40 metre cliffline in the way). We were not desperate, and fortunately the next day was raining rather than hot. 
Contributions are invited on this subject.

Water safety and Health

This is a popular subject on the newsgroup: how to ensure the drinking water is safe. The subject can get very technical (see flitration articles) Basically, the big hazards are viruses, bacteria like E coli, protozoa like Giardia lamblia, and chemicals from farms and dams.

That said, some medical people claim the biggest hazard of the lot is a failure to carefully wash your hands after going to the toilet, and that this rather than 'bad water' causes most illnesses in the bush.