or most of us, water comes out of a tap. But many millions of people have to walk many kilometres to a well and then carry the water home each morning, before their families can drink. For others, their only source of water is a dirty pond or river. One in every six of us – more than a billion people – do not have reliable clean drinking water.

However it comes, water is essential for people, for plants, and for animals. We need water to drink, to cook, to wash – and to flush the lavatory. We need roughly 50 litres of it every day to lead a healthy life.

And that does not include the water many communities need to irrigate fields and make their crops grow. In a lot of countries, watering crops uses up to 80 per cent of freshwater supplies.

For large numbers of people, especially the rural poor in developing nations, gathering water is an essential part of their daily routine. During the dry season, the nearest water may be an hour’s walk away. Often, children are kept off school to go and collect water for their families.

In shanty towns and poor urban areas, people may have to queue for hours to get water from a communal tap – or from a water seller, who may charge more for a can of water than richer people pay for a regular piped supply.

The United Nations says that the proportion of people without clean drinking water must be halved in the next 12 years. Governments promise to spend more to bring clean water to every community, alley and household. But many communities are doing the job themselves, sinking wells, catching rain from roofs and building small dams to stop rainwater running away.