The supply of treated water to homes and other buildings.

Water purification and storage.

The way a water supply works can be seen as comprising:
- a source or sources of supply,
- some kind of temporary storage, such as reservoirs,
- a means of transporting water from storage to the treatment plant, such as pipes or aqueducts,
- treatment facilities for improving water quality, and
- more pipes to carry the cleaned water to its consumers.

Water supply is extremely important to all countries and large amounts of money are spent on getting clean water to all homes. However, not all countries have enough money for this and many people in the developing world still get their water directly from rivers. As a result they suffer many more illnesses than people in wealthy countries.

Obtaining water directly from a river in Kenya.