Down the drain

Climate change is about pollution and that is easy enough to quantify with a glance skywards or taking a deep breath on a city street. The world's water crisis is not so simple for the amateur environmentalist to measure, though. Turn on a tap, and out it pours in a clean, uninterrupted stream, prompting the question: Crisis - what crisis?

Such evidence makes the alarm from scientists about water scarcity hard to swallow. They generally say that unless we change our ways, by 2025 more than half of the world's nations will face fresh water stress or shortages. By 2050, three-quarters of the global population may not have enough for its daily needs.

The convenience of city living easily shields us from such matters. We do not realise how fortunate we are; that one in three people on Planet Earth - two billion or so - live in water-stressed regions. They often do not have the convenience of plumbing, instead relying on streams and wells for their water. Global warming, pollution and population growth means that what they - and the rest of us - have is becoming increasingly rare.

During last century, the world population tripled, but water usage grew seven-fold. The number of people is expected to increase by three billion to nine billion by 2050, meaning we will need twice as much water. Earth's water supplies are finite; it is anyone's guess as to where the extra billions of litres that will be needed are to come from.

Governments are well aware of the risk of conflict over a lack of water. The precious liquid is as much part of the difficulties between Israel and its neighbours as religion and the right of sovereignty. But ensuring that there is enough is only part of the problem: it also has to be clean.

Every eight seconds, a child somewhere in the world dies from drinking dirty water. Half of hospital beds are occupied by someone with a water-borne illness. Contaminated water is implicated in 80 per cent of all sicknesses and diseases.