The Earth's precious life liquid

Water, the most precious liquid on Earth, is essential for life and constitutes 75 per cent of the mass of living things. There is no shortage of water on Earth but most of it is too salty for human consumption or for agricultural irrigation. There is a shortage of fresh water and this problem grows steadily worse as world population increases.

Waterworks were essential for the establishment and progress of human civilisation. The first settled communities were built where crops could be grown with the encouragement of rainfall and permanent rivers. Irrigation canals allowed greater crop production and longer growing seasons in dry areas.

As towns expanded, water was brought from increasingly great distances and complex engineering works such as dams and aqueducts were built. Nine major water systems with intricate distribution and well-built sewers supplied ancient Rome with as much water per person as is available today in many industrial cities.

Demand for water accelerated with the advent of the industrial revolution and the population explosion of the 19th and 20th centuries. Thousands of engineering works were built to control floods, to protect clean water and to provide water for irrigation and hydroelectric power.

Improved sewerage systems conquered once endemic diseases such as typhoid and cholera in the West. Cities sprang up in deserts, fed by water piped from far away. Forty per cent of world food production depends on irrigation and 20 per cent of worldwide electricity is hydroelectric.

Yet despite progress, half the population of the world still has a water service inferior to that of ancient Greek cities. The ballooning population in the developing world continues to intensify pressure on limited water supplies. More than a billion people lack access to clean drinking water and 2.5 billion have inadequate sanitation services. Preventable water-related diseases kill 10,000 to 20,000 children every day and huge cholera outbreaks still occur occasionally in Latin America, Africa and Asia.

The massive engineering works necessary to manage and distribute fresh water worldwide have forced tens of millions of people to move from their homes to make way for reservoirs. More than 20 per cent of freshwater fish species are endangered because dams and other works have wiped out the river ecosystems where they are adapted to live. The natural repositories for fresh water, groundwater aquifers, are being pumped out faster than they are being naturally replenished in many parts of the world. Shared water resources are causing tensions - and even violence - in places such as India and Pakistan; Israel, Jordan and Syria; and South Africa.

It seems strange that a planet, 71 per cent of whose surface is covered by water, could be suffering from a water shortage. However, 97 per cent of the world's water is too salty for human consumption or crops and much of the rest is out of reach; deep underground or in ice caps and glaciers.

THERE would be no water shortage problem if we could use ocean water and much research has gone into developing desalination methods. Reliable methods exist but the expense involved puts this technology out of reach of all but the wealthiest countries such as Saudi Arabia.

Water planners are now thinking differently about how to solve the world's water problems. An important factor in this new thinking is to devise ways of using existing water supplies more efficiently, thereby stretching them further. This philosophy is already showing results. Agricultural irrigation accounts for two-thirds of water used worldwide. Traditional methods are very inefficient and new methods such as drip irrigation can reduce water demand by up to 50 per cent.

In the US, water withdrawals from aquifers have fallen by more than 20 per cent from their peak in 1980. Development of new industrial technology can also help. Producing a tonen of steel prior to 1950 required 60 to 100 tonnes of water, whereas modern technology now uses less than six tonnes of water.

There are many simple ways in which water can be used more efficiently. In many countries, more than 30 per cent of domestic water supply never reaches its intended destinations because it leaks away through faulty pipes. Mexico City loses enough water to cater for a city the size of Rome, but, even in more modern systems, losses of 10 to 20 per cent are common.

We are very wasteful of water in our homes. Before 1990 in the US, each toilet drew six gallons of water for each flush. In 1992, a national standard was passed limiting the flush in all new toilets to 1.6 gallons, a saving of 70 per cent. On this side of the world, the average flush is now about one gallon, down from a previous two gallons. Mexico City replaced 350,000 old toilets with low-flush toilets and saved enough water to supply an additional 250,000 people.

There are many other ways to reduce water usage, including better leak detection, less wasteful washing machines and so on. Undoubtedly severe water problems are on the cards for some parts of the world, but a crisis can be averted if we develop all the solutions available. For a detailed look at the world water situation, see Scientific American, February 2001.

William Reville is Associate Professor in Biochemistry and Director of Microscopy at UCC