(AP) It's not only our carbon footprint we should worry about. Experts are looking for solutions to our growing water footprint, as urban populations explode and the demand for biofuels adds stress on water for farmland.
Nearly half the people on Earth, about 2.5 billion, have no access to sanitation, many of them in urban slums. The world's cities are growing by 1 million people a week, and soon their aging water systems will not cope.
"What we are doing now can't keep up with the issues we already have," says Carol A. Howe, an expert working for a UNESCO-led water development project called Switch.
"Something needs to change. It needs to change quickly, and it needs to be fairly dramatic," she told a symposium of journalists Wednesday.
The threat of climate change has drawn attention to carbon footprints, the amount of greenhouse gases produced by human activity. Now scientists have begun calculating a water footprint, the amount of water needed to produce goods or services.
A report published this month by UNESCO-IHE, the Institute for Water Education in Delft, says it takes 70-400 times as much water to create energy from biofuels as it does from fossil fuels.
It said the production of crude oil requires slightly more than one cubic meter of water for one unit of energy, compared with 61 cubic meters to grow biomass in Brazil _ mostly sugar used for ethanol _ for the same amount of energy. The water footprint of biomass grown in the Netherlands is 24 cubic meters, the report said.
Engineers are experimenting in a dozen cities from Lima to Beijing to find ways to ease the pressure on water resources.
The pilot projects, run by the U.N. Education, Scientific and Cultural Organization and funded by the European Union, range from turning rooftops into gardens, capturing and recycling rain, recharging underground water reservoirs with waste water, and swapping traditional flush sanitation for dry toilets.
The English city of Birmingham is monitoring the effects of green roofs to reduce flooding during storms, to cut energy needs and to study how to capture run-off to reduce water needs in the buildings or surrounding areas, Howe said.
A project in Tel Aviv, Israel, channels treated waste water into the aquifer through the natural filtering system of the soil, and is testing whether it can be reused for drinking water, she said.
Gary Amy, a professor of urban water supply and sanitation with UNESCO-IHE, said the United Nations is almost certain to miss its 2015 goal of halving the percentage of the world's population who lack adequate sanitation. The goal takes 1990 as the base level.
Accounting for population growth, some 500,000 new people every day would have to be connected to a sanitation system to meet the U.N. target, he said.
Waterless toilets, using either chemicals or composting, are being tested in Ghana, Kenya, Peru, Egypt and elsewhere. They also enhance the possibility of separating human waste, using liquid waste as a rich source of nutrients for crops, Amy said.
"If we captured all the urine in Africa, it could match all the nitrogen and phosphates used for agriculture," he said.
Howe said standard mechanisms consume about 25 percent of all residential water _ drinking water that is literally flushed down the toilet. "It takes a lot of energy and money to bring in the water, to treat it, to put into the toilet, to treat it again, and to put it into the river system," she said.