Humans need approximately 3 litres of water every day for biochemical reactions in our cells and to replace that lost by exhaling moist air, sweating and of course producing urine and faeces.

Add to that water needed for washing, cleaning your teeth and shaving - that is a considerable amount of water needed each day.

But in space, the cost of transporting so much water is huge. Collecting water lost from the body and purifying it so that it can be re-used is therefore desirable.

This may sound outrageous - and even dangerous - but extracting water from urine is actually done naturally in your body when you are thirsty using a protein hormone known as ADH (anti-diuretic hormone, also known as vasopressin) which acts on the kidneys.

Urine contains urea - an excretory product from the breakdown of amino acids in the liver. Read more about urea here.

How do the kidneys make urine? - Here is an excellent tutorial

So, by filtering out all the poisonous wastes, such as urea, from urine, scientists hope to produce water that can be recycled - I wonder what it tastes like?

Read an update report on 25 November 2008 in the Independent