There is a decades-old adage that the tap water Londoners sip has already passed through seven other sets of human kidneys. The principle is at least partly true.
About 80 per cent of the English capital’s drinking water is drawn from the rivers Thames and Lee, and just 20 per cent from aquifers — the large, natural underground stores that are deep in the ground and absorb rain run-off.
Although the rivers are fed by rainwater, they also receive untreated effluent via some of Thames Water’s 354 sewage treatment plants when it is pumped into the rivers via the combined sewage overflow pipes that stop housing flooding when the network is overwhelmed. Water from the rivers is taken and processed for human consumption at one of the utility’s five big water treatment facilities.
Now there is a move worldwide to recycle sewage into potable water, without it being pumped into a river or aquifer first. The public is often reluctant, but supporters insist the process is safe and not greatly different from treating water from a river or reservoir.
“We already drink recycled water,” says Christopher Gasson, chief executive of research publication Global Water Intelligence and member of the 2030 Water Resources Group, the World Bank’s global committee pushing for sewage recycling. “The distinction between whether it is freshwater or wastewater going into the drinking water treatment plant is largely academic.”
While some countries, such as Switzerland, have large amounts of water to draw from, others increasingly suffer shortages and are forced to pipe in water from far away or use more innovative methods — such as recycling sewage.
Data centres, robotics and thermonuclear electricity generation are all increasing the demand for water, and sewage recycling is one of the cheapest ways it can be delivered.
Some 8 per cent of sewage globally is recycled directly into drinking water at treatment plants without being pumped into rivers and underground aquifers first. But the Water Resources Group launched an initiative this year aiming to increase that amount dramatically.
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“The economics are behind treating sewage,” says Gasson. “You can treat sewage to whatever level you like, either for industry, or to make it drinkable, and it’s by far the best way of guaranteeing water security.”
Diverting distant rivers to new reservoirs is expensive and requires millions of pounds of finance upfront. So too does seawater desalination, which costs nearly twice as much as recycling water from sewage.
But the biggest reason that treating sewage is cheaper is that water is heavy and expensive to transport, so creating a source of drinking water close to where it is needed makes sense. “Around 80 per cent of the cost of water comes from moving it around, whereas, if you create a source exactly where it is used, it’s incredibly efficient and much cheaper than alternatives such as desalination,” says Gasson.
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The process is not untested. The leader in the field is Windhoek, capital of Namibia. Its Goreangab Water Reclamation Plant has been making direct potable use of treated wastewater since 1968. That was four decades before anyone else, notes Professor Asit Biswas, an expert in water at Glasgow University.
Singapore has been recycling water from sewage, dubbed NEWater, since 2002. The NEWater is purified to a high enough standard that it can be used by local silicon wafer factories, says Biswas. The remaining 10 per cent is pumped into reservoirs for drinking water.
Last year US space agency Nasa said 98 per cent of wastewater on the International Space Station was being recovered under a new system. It distils anything from urine to sweat and breath moisture into water that is safe to drink.
However, any increase in the direct transformation of sewage to drinking water must overcome a substantial public perception barrier.
“Technically, the wastewater problem has been solved,” says Biswas. “But
the perception problem still needs to be addressed, not by engineers but by behavioural economists and physiologists.”
There are signs that this may be changing. German consumers can buy beer made from recycled urine, the result of a tie-up between the city of Weissenburg, US water-tech company Xylem, and the Technical University of Munich.
In 2023 California’s State Water Resources Control Board adopted regulations to allow water utilities to start developing facilities that put highly treated recycled water straight into drinking-water supplies.
“Desalination is very expensive in California because of the environmental restrictions,” says Gasson. “And for that reason they are favouring reuse, which is by far the cheapest means of topping up the reservoirs in the face of drought.
Nevertheless, people remain nervous. In Britain, campaigners are railing against sewage recycling schemes planned in London and the Southeast of England.
Biswas says concerns over recycled sewage are “scientifically unfounded”, but he is equally insistent that water companies should “treat wastewater properly if the ecosystem and human health are to be preserved”.
Then, he says, “society will have access to new sources of water.”
