A similar question to ‘how long can you live without food‘, but with some key differences. Your body is able to store energy to some extent as fat, meaning some people can survive without food longer than others. The body cannot store water, so the answer to how long you can survive without water will be much more accurate and consistent. So, assuming you, right now, a perfectly well hydrated person with clear urine is no longer allowed water, how long would you survive?
I’m going to make some reasonable assumptions to make this easier – you are in a moderate climate so won’t be sweating excessively, you are well fed and hydrated for, you won’t be doing any exercise and you are not elderly or an infant. Essentially, if you will be doing nothing which causes you to lose excess water.
Well, unsurprisingly there is no specific research for this, because it would be very cruel (not to mention illegal) to do this kind of research. In fact, most researchers agree that there is too little known about how much water we need and what our requirements look like.
The best answer I can get from a scientific body is the complete absence of water ‘will be lethal in a few days‘, which anyone could have guessed, and is quite vague. Further digging around and I’ve found that the general consensus is that you can only live 3-4 days without water before you die. In hotter climates, or if you are exercising, this could be as low as 1-2 days, but it depends on the climate and the exercise you are doing. In normal conditions which I described above, it is 3-4 days. However, you won’t just feel normal and then drop dead, you will steadily feel worse and worse as you go through the stages of dehydration.
Most people will be familiar with the symptoms of early dehydration, and they are easily reversible but drinking some water. These usually will kick in a few hours after drinking when your body has lost roughly 2% of its total fluid. These symptoms are:
Symptoms of moderate dehydration will kick in when you have lost about 5% of your fluid, and these symptoms will probably develop over day 2-3. These symptoms are:
The symptoms of late stage dehydration will occur when you have lost about 10% of your fluid, and will start to develop through days 3 and 4 without water. The symptoms are:
It would be great if water wasn’t so essential to body functions, maybe then we could survive longer without it. Sadly, water is needed for pretty much every that goes on in the body. One of the first signs of dehydration is dark urine, and this is because water is needed to transport waste chemicals such as urea out of the body. As water gets lost through urination, respiration and perspiration, the amount that the body can afford to lose decreases, meaning more is lost through urination, which is the greatest cause for water loss. This is far from fatal though.
If dehydration continues, less and less water will be filtered out of the blood as urine, which can put a lot of strain on kidneys. Your blood volume will also decrease because water is a major component of blood. This reduced volume puts strain on the circulatory system, particularly the heart, which increases heart rate to try and compensate for the loss of water. The reduced volume also causes the blood to becomes thicker, which leads to difficulty in providing nutrients to parts of the body, which can cause tiredness, tingling in extremities and poor physical performance. Also, as a healthy brain is about 73% water, the brain will start to become dehydrated, which can cause fuzzy thinking. You may recognise all these symptoms are part of moderate dehydration, and although it’s not fatal just yet, you can start to see that functions in the body are struggling.
Breathing also increases to try and compensate for the reduced blood volume,, and usually the body temperature will rise due to reduced sweating.
As dehydration continues even further, important biological systems start to break down completely. The volume of the blood becomes even lower, putting even more strain on the heart, and even the heart is struggling to get enough water for it to function properly. This will become too much for the heart and will lead to nutrients not reaching muscles in limbs, which can cause muscle spasms. More and more water will be lost from the brain, which will further affect thinking, and ultimately cause unconsciousness. Eventually, the heart will no longer be able to function, and is usually the cause of death from dehydration.
Although there is not a great deal of research into this, it is generally accepted that you can’t survive more than 3-4 days without water. During this period, many biological functions will start to fail, but the cause of death from dehydration will be heart failure.
Image courtesy of John ‘K’