Cloe Williamson of Balclutha Primary School asks :-

Why do people need to drink water?

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

The answer is that some water intake is essential for us to go on living. We lose water continuously from our bodies by evaporation from the skin and lungs, and by sweating. We also have to make urine, because metabolism of proteins makes nitrogen-containing poisonous compounds like ammonia and urea, which must be eliminated from the body in water. This loss of water must be replaced by drinking.

If we don’t have access to water, as in the desert, then we would become gradually dehydrated. The blood would become more viscous, making it harder for the heart to pump, and the increased concentration of salts in the body would kill us. We normally need about one and a half litres of water each day to replace that lost. Drinking more than this is not usually a problem, although it gives no real advantage.

The kidneys can make dilute urine to get rid of the excess water. However, there is a small danger, since urine must always contain some salt. Normally we get the replacement salt from the diet, but if we drink a lot of water and eat a low salt diet then we can become salt depleted. Incidentally, nearly all animals drink only when they become dehydrated, and then only to restore the deficit.

Only the primates drink as a social activity and become overhydrated. Nothing to excess is a good way of life!