Why water?

This may seem like an obvious answer but the question is often asked: Why do we need water to survive?
Humans are made up of between 50% and 70% water and amazingly the brain contains over 80% water. Therefore if we do not take in water on a regular basis then we will lose body fluid and become dehydrated.
This is obvious as we lose water by perspiration and removing body waste, toxins etc. Without water to flush out body toxins then we will become ill very quickly. Even in an ideal situation we cannot survive without water for more than 3 or 4 days. If the climate is more extreme or we have to exert ourselves then this could be much less.
So while we can go without food for extended periods we cannot go very long before we need to take in water. Lack of water will lead to dehydration, illness and death. Drinking unclean water can kill just as easily. So after we find a safe environment to survive then water is the next most important consideration.
The body cannot store a reserve of water as it can food and yet water is needed to allow the bodies cells to function. Lack of water is a most serious threat to survival once we have achieved a safe situation. Water can be drunk but also most foods unless dehydrated will contain a significant proportion of water and this will add to our water intake.
Water then is synonymous with life.