Devon Allen of Balclutha Primary School asks :-

Why is water healthy for us?

John Leader, a physiologist at the Otago School of Medical Sciences, responded.

Without water we would become gradually dehydrated and die. Not only do we lose water by evaporation, but the kidneys have to make urine to get rid of water-soluble toxic compounds.

Human kidneys can concentrate urine to a little more concentrated than sea water, but not enough for us to be able to drink sea water and survive. Marine mammals like whales can make very concentrated urine so they can drink sea water. Many seabirds and reptiles like turtles have a special gland near the eyes which can make a solution more concentrated than sea water, and it is secretion from this gland which gives rise to the expression “weeping crocodile tears”!

All the chemical reactions which are a feature of life take place in watery solution. If the water is removed these reactions cannot occur, leading generally to death. A very small number of tiny animals can be dried out and enter a state of ‘suspended animation’, where they can remain indefinitely, coming back to life when water is restored. Researchers are trying to find out how this is done, since it offers possibilities for storing human organs for transplants, and even perhaps animals threatened with extinction.