How Much Water Should I Drink In A Day?

I have discussed at length the priorities of survival and emphasised the importance of water in a survival situation, so today I have a short post on the subject of staying hydrated and I answer “how much water should I drink in a day”. I also give you some tips for making sure you are taking on optimum volumes of water.

The first thing I want to look at is the myth that “the body needs to consume 2 litres of water a day.” This sentence was actually twice as long and missed a crucial element off of the end. It should read – “the body needs to consume 2 litres of water a day; however the majority of this can be obtained from food.” Call me a cynic but I am convinced this was a deliberate ploy by mineral water companies to encourage you to drink more bottled water…

How much water should I drink in a day then?

So with that requirement explained I want to drill down a little more into what the body actually requires on a daily basis. As a guide, an adult male loses the following volumes of water every day when idle. The daily water intake calculator below should give you a rough idea of what to expect. Bear in mind this is on average and everyone is different.

How much water should I drink in a day then

I cannot stress this enough, these are the water losses whilst idle; that means sitting doing nothing, just sitting and waiting. There are several things that will increase the water burden on your body and will ultimately affect your hydration levels and chances of survival.

What causes my water needs to increase?

You have seen from the daily water intake calculator that there are some losses that are inevitable there are other factors that will cause these losses to increase.

Eating food – This is another reason that food is not important in a short term or water critical survival situation. Digestive processes require water for the process itself and to secrete waste. Eating carbohydrate has the smallest water burden and is more easily digested due to Amylase, an enzyme which starts digesting carbs in the mouth.

Fat and Protein are more complicated molecules and are broken down in the gut by the enzymes Protease and Lipase respectively. Protein and to a lesser extent, fat, produce a lot more waste products which means greater volumes of urine.

Movement – The more you move the more you sweat and breath. This causes more water to be wasted in sweat and respiration.

Injury – If you or others are injured then the process of being in shock and/or blood loss may cause water requirements to be significantly higher.

Environmental factors – Heat and humidity are the 2 greatest factors here. The warmer it is the more you will sweat. The closer the air temperature gets to body temperature (around 98F or 37C) the more difficult it is to use sweat as a cooling mechanism. Once the air temperature gets above your body temperature then you are on the back foot and your sweat production will increase a lot to compensate and prevent you overheating.

Humidity is similar, the closer the relative humidity (RH) is to 100% the more your body has to sweat to maintain a safe core temperature. If high humidity and high temperature are both present then life becomes really difficult.

The worst environment I have operated in is the jungle which was 80 – 95% RH and 85 -95 F (30 -35C). I had to drink around 12 litres a day to maintain my hydration when idle. Surprisingly, in the Middle East in 50% RH and 113 F (45c) I was better hydrated and it felt less oppressive because of the much reduced requirement to sweat. I could get by on around 6 – 9 litres of water a day.

Fitness and body size – If you are 50 lbs heavier than you should be then that is 50 lbs worth of extra effort required to carry it around. The chances are that the extra 50 lbs are not muscle either which means carrying 50 lbs of insulating fat making it a lot more difficult to regulate body core temperature.

Fitness and body size

If you are in shape and exercise regularly the chances are that your body is an efficient sweater and is in good condition which helps all body processes work more efficiently. There is one exception to this rule; body builders. Unfortunately for these guys they will be in a world of hurt if water is short. They will have a huge water need due to their bulk (weight) and large muscle content.

What can I do to stop dehydration?

There are several things that are worthwhile doing that will help you stay hydrated until rescue arrives.

  • Do nothing
  • Sip water
  • Don’t eat if water is scarce

The single most important action you can take is to ration sweat not water! I will say that again just to stress the importance, ration sweat, not water! Very simply, do as little as possible in order to survive. The more you move, the more you sweat and the more water you need to replace. Even a small increase in activity can cause a 25% increase in water loss from the body.

Listen to your instincts, nature knows best!

Get in the habit of sipping water and not taking big gulps as the body can only absorb an absolute maximum of around 1 litre of water per hour. If you consume too much your body will just pee it out nd it will be wasted.

Dont drink out of habit, drink according to what your requirements are. In the western world where we are bombarded with mineral water adverts, far too many people are in the habit of over consuming water. Most people who do this drink out of habit rather than any bodily indications.

UPDATE 28 Jan 2017 – Stumbled across this article from the BBC on how important water is to performance and how much we actually need to drink in a day

First world problems – stop being so greedy

In a survival situation if you over consume then essential vitamins and minerals are flushed from the body quicker than is necessary. This means you have less ultimate survival time if these are not replaced due to lack of food.

First world problems – stop being so greedy

Despite what mineral water companies would have you believe, thirst has served humans well for 2 million years. The notion of thirst being unreliable makes no evolutionary sense, if it wasn’t then humans would have died out when they were still evolving from fish. A key way of recognising the early signs of thirst is licking your lips more frequently than normal.

I want you to stop and take a second to think about thirst as this as its important. Zebras on the Serengeti do not have adverts from the Serengeti Mineral Water Company telling them to drink more water, yet somehow they manage just fine… Weird eh? Come to think of it neither do Masai Warriors living on the African Plains. DONT BE SUCKED IN BY MASS MARKETING!

The real issue is that most people over consume water and don’t actually know their own bodily signs. Conduct an experiment for a week, drink when you feel your body is giving you signs to drink, don’t do it out of habit. You will surprise yourself just how little you need to stay in equilibrium.

Everything in moderation

Taking in too much water can be fatal as Sodium is flushed out in the urine, this is known as Hyponatremia. Sodium is an essential salt that is used by the body for life supporting functions like nerve signals, muscle contractions and regulates blood pressure. I have witnessed a victim of Hyponatremia, he ended up having seizures, vomiting and severe and extremely painful muscle cramps. Not nice to watch.

The final point is ensure you stop eating if you are short of water as food digestion will increase your water needs. How long can you survive without food? Well it’s around 30 days or so if you are fit and well and don’t succumb to disease or illness.

What are the key indicators of dehydration?

What are the key indicators of dehydration

The following table has some of the symptoms of dehydration. A point to note is that mild dehydration may not have many symptoms at all other than thirst and a slightly dry mouth. One key indicator of mild dehydration is licking your lips, if you are doing this with no reason then you are probably mildly dehydrated.

The key points to take away

  • Don’t over consume water
  • Don’t eat if water is scarce
  • Thirst is accurate if you understand your body
  • Try to drink less for a week and only when you have cues from your body to do so.

Thanks for reading, hopefully that has been an insightful post and given you something to think about. If you enjoyed this post then please have a look at my others as there are plenty of other great articles here on

If you enjoyed this then I would really appreciate if you would share it far and wide or comment below.

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