“Water, water everywhere… but how much should I drink?”

I have never been in a situation where I have had to go without water for more than a day, perhaps ten hours or so. I was active during these ten hours which exaggerated the associated sensations (fatigue, head ache, weariness) and I would not wish to find out, other than in a controlled exercise, what it is like to go for days without any water at all.

When considering the minimal amount of water required in a day, I was very interested recently when shown a sachet of water from a life raft survival/emergency kit. It held 500ml of purified water and suggested that this be the daily minimum amount consumed.


This was a British product and I was informed that a comparative American product only contained 250ml of water. Perhaps Americans require less water? When I was at University, studying exercise physiology, I read numerous articles which recommended a minimum water intake of 2 litres.


Wiseman (2009) suggests that it is possible to stay healthy in a survival situation with a minimum of just 1 litre of water consumed per day. He also states that it is possible to survive on 55-220cc of water per day, although this would require certain environmental circumstances and a drastically reduced work-rate.


Wiseman (2009) shows a rationing plan for survival at sea (presumably meaning that in a life raft one can assume that activity levels and food consumption would be low) which states:

Day 1: NO WATER. The body is a reservoir and has a store.

Day 2-4: 400cc if available.

Day 5 onwards: 55-225cc daily, depending on climate and water available.


Towell et al (2009) states that a minimum of 3 litres per day is required in a survival situation to stay healthy, due to the high volume of activity required to create protection, be located, acquire food and water or navigate to safety etc. Towell et al (2009) also seems to disagree with the trend of recommending that no water be consumed for the first 24 hours, in line with the typical rationing plan. This is justified by the reasons outlined above (high volume of activity) and that it could be counterproductive to allow yourself to become dehydrated at the beginning of a survival situation.


To summarise I have found that there is a great variety of information on this subject which tends to be contradictory in nature. Another useful source of information on the subject comes from the World Health Organisation. W.H.O. carried out research in order to assist aid organisations, such as The Red Cross, in supplying vital support to people in crisis due to natural disasters, warfare, famine, etc.


The following diagrams are taken from a WHO document entitled ‘How much water is needed in emergencies?’



Of particular interest to me is the comment related to the daily requirement of 2.5 to 3 litres of water per day, for drinking and food, which states ‘depends on climate and individual physiology’. I would add to this comment; ‘depends on climate, activity level, stress level, protection from environmental circumstance and individual physiology’. Also of interest is that hygiene practices and cooking needs are not given the prefix ‘survival’. This would appear to be in-line with Towell et al (2009) suggestion of 3 litres per day, when active.


I would estimate that if a person was sedentary, in quite stable climatic circumstance (where it was relatively easy for the body to maintain homeostasis without excessive need of extra water, i.e. NOT the desert), was not excessively stressed by their predicament, had protection from environmental factors which might exaggerate water requirements (wind, direct sunlight etc.) and had the personal physiological make up which did not require excessive amounts of water that 1 litre of water per day would be a comfortable amount for survival. This estimate is based upon a mean amount taken from Towell et al (2009), Wiseman (2009) and W.H.O.’s suggestion, which I then reduced a little as most water bottles, which outdoor users carry, hold 1 litre.


I carried out some experimental research recently as I had a day over the holidays when I had to wait in for a delivery. I used the time (and an army 1 litre water bottle) to try out my theory. I limited my food intake to a few slices of bread, just to stave off hunger pangs, and didn’t find it too uncomfortable to ration the 1 litre of water out over the period of 24 hours.


However, I would imagine that even with just a little exertion, through activity or an inclement climate, would prove 1 litre to be insubstantial. I’d drink as much water as possible which when in the field, and having to find, filter and purify it, never seems to be enough! “Water, water everywhere… drink very drop that’s safe!” My opinion.


Thanks for taking the time to read this post.


©Andy Lewis 2017