Water is a limited and expensive resource on board the ISS. The reason for this is that there is limited storage space for water and there is no continuous water supply. It has to be brought to the ISS from Earth. It can be transported by various launchers, or can be provided from the Space Shuttle where water is produced when the fuel cells on board the Space Shuttle combine oxygen and hydrogen to make electricity.

	2 H2 + O2 → 2 H2O + energy

The

Water storage on board the ISS

ISS life-support system on board is designed to recycle as much water as possible – even urine and the humidity in the cabin air. And to minimise the consumption of water, its use has to be as efficient as possible. For example, a shower on Earth takes about 50 litres – an astronaut, however, would use less than four litres for personal hygiene and not more than 10 litres of water in total per day.