Functions of Consuming Water

Amazingly water makes up about 60% of an adult's body weight, that's why you'll have bodybuilders and boxers wearing sweat suits prior to weigh-in, to achieve a lesser body weight, or, more commonly, wallys who want to weigh less (but only until they're re-hydrated again!!).
Our water must be continually replaced in order to stay hydrated, aid digestion, lubricate joints, excrete waste & transport other nutrients around our body.
An example of how much water we use: through breathing alone we'll expel about 1/2 pint of water a day.
Of course, if the weather's hot or we're exercising vigorously, both sweating and breathing faster will mean we'll lose even more.
Not consuming enough water daily or excessive loss (dehydration) can lead to some serious ailments, even death.
Commonly we're often told that we should consume around 3 liters of water a day (GP note: This does though depend on many, many variables - food intake, size, activity, heat, hydration level etc..
).
About a month ago, the most annoying marketing tripe was on every channel, saying that if a sedentary individual were to consume enough fruit, vegetables, and cups of tea during the day, this should suffice for their water intake.
No sh*t!!! Fruit & veg are 75 - 95% water, whilst tea is made with water.
Also, the majority of non-processed food we eat contains a large percentage of water.
Sea mammals for example, such as a dolphin, do not stay hydrated on sea water, as the salt water would actually dehydrate them further (the body using existing bodily water to dilute the intake).
Instead they stay hydrated through their food, fish.
Most fish being 75 - 85% water.