UNDER THE MICROSCOPE:Climate change means that water conservation will become ever more important in the future, writes Dr William Reville
FRESH WATER for drinking and cooking is something we take for granted in Ireland. Unfortunately, many parts of the world do not have such plentiful supplies, and the situation is expected to worsen as populations grow and the effects of climate change kick in. Even here in Ireland we will have to conserve fresh water supplies more carefully in the future. The global water situation is outlined by Peter Rogers in the August 2008 edition of Scientific American.
The sheer familiarity of water masks its enormous importance. Living organisms are predominantly composed of water - yes, even Bono is 70 per cent water! All chemical reactions in the body take place in water and you would die far sooner if deprived of water than if deprived of food.
The International Water Institute, Stockholm, reports that the average person needs 1,000 cubic metres of water annually (40 per cent of an Olympic-sized swimming pool) for drinking, hygiene and growing food for sustenance.
It is a challenge to meet this demand in drier developing parts of the world with large populations, eg the Nile and the Ganges now regularly run to a trickle for periods during the year. Shortages of fresh water caused by droughts are also becoming common in the developed world.
Rogers reported that 110,000 cubic km of water falls from the sky onto the earth each year. About 61.1 per cent of this (green water) is absorbed by plants/soil and is not available for capture/storage because it evaporates back into the air.
Another 33.8 per cent of total precipitation (blue water) collects in rivers, lakes, wetlands and ground water and can be tapped before it evaporates or runs into the ocean. The biggest human use of these free-flowing waters is farm irrigation (6.5 per cent), and only 0.1 per cent is used by cities and industries.
Much of North and South America and northern Eurasia receive abundant water supplies today. Central Africa and parts of India suffer from economic water scarcity (poor technical training, weak finances, bad government) where access to water is limited even though sufficient supplies are available. However, a combination of population increase and climate change could seriously exacerbate the situation by 2025 in the Americas and in Europe.
Rogers reports on a number of measures that should/can be used to conserve and make better use of scarce water in the future. Charging more for water is near the top of his list. Freshwater on this side of the world has traditionally been priced so low that users have had no incentive to save water. The income generated would allow water utility companies to improve the water processing infrastructure, to prevent leaks and to conserve.
Another high priority would be to conserve farm irrigation water. A 10 per cent saving here would save more than used by all other consumers - plugging leaks, using drip-irrigation methods and using crops that can withstand low moisture.
"Virtual water" is the amount of water used to produce a product. Food is very high in virtual water - it takes 1,000 litres of water to make 1kg of wheat. Growing food is an enormous pressure on water in an arid country and, so, importing this food means the inhabitants of the arid region can conserve scarce water. This can also be important in international relations. For example, Rogers reports that importation of virtual water by Jordan reduces the chances of water-based conflicts with neighbouring Israel.
Low water sanitation also conserves water. I was in Munich recently and noticed that the toilet in my hotel had two flush buttons - one for low volume flush to deal with a piddle and the other for higher volume flush to deal with more substantial matters.
Indeed you can go much further with toilets. Systems are under development that separate the urine from excrement. The urine is collected in a tank and used as liquid farm fertiliser. The excrement collects in a bin where it is broken down by microbes into a non-toxic nutrient-rich substance that can be used as crop fertiliser.
As much as 97 per cent of the world's water is salty, so, if we had a cheap easy way of removing the salt we would have few remaining problems with scarce fresh water supplies. Desalination technology has been expensive but recent developments have substantially reduced costs for the most energy-efficient technology - membrane reverse-osmosis systems. This will allow many coastal cities to access new and secure sources of fresh water. Rogers is optimistic that we can avoid a global water crisis if we quickly adopt existing ways to conserve and enhance water supply.
Finally, you have all heard of the carbon footprint. Well, you also have a water footprint - the volume of freshwater you use directly and in the provision of the goods and services you consume. You can look up your water footprint at www.waterfootprint.org.
• William Reville is associate professor of biochemistry and public awareness of science officer at UCC -http:// understandingscience.ucc.ie