Desalination is often dismissed as being expensive and polluting. But advances in tech are putting it back on the agenda

It’s tipped to be the key environmental challenge of the century – and there’s plenty of competition for that accolade. Water. The planet has plenty of it, but most of it is unusable, locked up in salty oceans. But demand is soaring and the strains are starting to show, from China to Latin America, India to California.

Almost a billion people lack access to clean water, and the forecast is for this number to grow sharply in coming decades. Last year, Cape Town came dangerously close to running out of water. Even rainy England has been told: carry on like this and you’ll run out of the stuff in 25 years.

There are no easy solutions – but one technology that has proved controversial in the past may be on the cusp of a new dawn. Call it desalination 2.0. Freshwater supplies are under increasing pressure across the world, with the 4 billion people currently living in water-scarce areas predicted to rise to 5 billion by mid-century. Climate change, growing populations and our consumption habits are all key factors, while the technology we use relies on groundwater being extracted at a faster rate than it can be naturally replenished, which just stores up problems for the future.

The process of converting seawater to something less briny that could be used on farms and in homes has long been viewed as a last resort for meeting our water needs. The technology is expensive, energy-intensive and only suitable in some areas. It also generates a potent byproduct: highly salty brine, which is usually released back into the sea, and the process has the unfortunate effect of disrupting local fish populations by sucking them into the inflow. But could desalination be reformed enough to make it a viable solution to our water needs?

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David Binns of early-stage innovation company Epicuro believes that advances in renewable energy technology could make small-scale desalination units a revolutionary advance for poor communities in the developing world, particularly in hot countries. “It’s a life-saver,” he says. “It could make an enormous difference to a terrible problem.”

In a prototype he co-invented with seed funding from the drinks and property tycoon Howard Raymond, Binns uses solar collectors which heat water to boiling point, then condense it separately from the salt or dirt that rendered it undrinkable. A small photovoltaic system is attached to power the processors necessary to regulate the machine. This method can be used not just for desalination, which requires the users to be near the coast or another source of saltwater, but also in areas where water is available but grossly contaminated, which involves a much bigger slice of the global water-stressed population.

Binns is now seeking government and charitable partners to make the technology widely available, and estimates that between £2m and £3m would enable the company to start manufacture. He envisages the devices being used on a small, local scale, with each unit enough to supply the drinking-water needs of an average family.

Desalination: the quest to quench the world's thirst for water Read more

Other innovators are also exploring the possibilities of renewable energy, as one of the biggest handicaps for traditional desalination is its huge consumption of fossil fuels. For instance, US engineering and technology company Honeywell has supplied water stations (which clean water contaminated with fluorides, nitrates and salinity to 480,000 people) in India, where as much as 70% of water supplies are contaminated and 200,000 people die each year from lack of access to safe water. Along with Safe Water Network India, Honeywell has installed 150 stations that rely solely on solar energy.

Newer technology is also coming to the assistance of desalination advocates. The wonder substance graphene is inevitably one avenue being explored. A graphene “sieve” was created two years ago at the University of Manchester which cleans salts from brine and, if it can be scaled up, could be used for cheap desalination. Reporting on the work in the peer-review journal Nature Nanotechnology, Professor Rahul Raveendran Nair said: “Realisation of scalable membranes with uniform pore size, down to the atomic scale, is a significant step forward and will open new possibilities for improving the efficiency of desalination technology.”

Facebook Twitter Pinterest ‘Israel holds the crown for long-term investment in the technology as a strategic public service.’ A transportable desalination system in Hadera. Photograph: Nir Elias/REUTERS

Separately, the British company G20 is working on an alternative way of using graphene oxide filters for desalination, with a process used to apply a coating of graphene oxide to existing polymer-based water filtration membranes.

More traditionally, the $1.75m XPrize Water Abundance was awarded last year to technology that uses distillation to take the water content out of humid air. Skywater machines use a distillation process to turn water vapour to liquid, then treat the water with ozone to prevent contamination with micro-organisms. The more humid the air, the more water can be extracted. However, the technology is still expensive, with prices of $18,000 (£14,000) to $28,000 for units that can process up to 300 gallons a day.

For some large urban areas, desalination offers an urgent way out of an increasingly pressing problem. Cate Lamb, the director of water security at CDP, which measures companies’ environmental performance, points to the success of Cape Town, which last year managed to stave off the worst of its water crisis by investing in desalination, as well as restricting water use.

Some businesses are also investing in the technology on a smaller scale to supply their operations in water-scarce regions. Lamb says: “Desalination is already having a role to play in aiding cities and companies to respond to water challenges. The deployment of the technology in Cape Town is one of the primary ways in which the city is aiming to enhance resilience.”

A recent positive report by financial analysts at Moody’s Investor Service found that the success of Cape Town’s desalination, along with demand management and increased investment in water, was paying off in economic growth and stability, too. “A resilient water sector is critical for the health of Cape Town’s economy and the city’s fiscal position,” said Zoe Jankel, senior analyst. “New investment will enhance that resilience.”

Facebook Twitter Pinterest A farmer uses desalinated water to tend to his crops in the Atacama desert, Chile. Photograph: Martin Bernetti/AFP/Getty Images

If Cape Town is the most recent prominent example of desalination being used to plug an urgent gap, Israel holds the crown for long-term investment in the technology as a strategic public service. The country is home to the world’s biggest reverse-osmosis desalination plant, and can now produce more water than it needs from desalination and water recycling. This could potentially allow for freshwater exports to the surrounding region, and more importantly for the export of “virtual water” – that is, agricultural goods from vegetables and grains to clothing fibres, and manufactured products – to boost its economy.

As much as 80% of Israel’s drinking water comes from coastal desalination plants, depending on the time of year and the weather. This is proving so energy-intensive that the biggest plants operate mainly at night, to avoid overloading the power grid. Crucially, however, the country has also invested heavily over decades in the treatment of waste water, recycling nearly 90% of its waste water through sewage treatment plants which then redirect the treated water to irrigation.

Even with advances in desalination technology, there will still be drawbacks to its widespread use

The sludge byproduct is also used as fertiliser and to generate biogas. This strategy highlights the need for desalination, as it is in Cape Town, to be integrated into an overall water management plan. There is no point in relying on such an expensive way of generating water while wasting the resource in other ways.

But where desalination is used without renewables on a large scale, there are always accompanying problems. “It does come with a cost – a carbon cost,” says Lamb. “Further, there are risks associated with the discharge of the large quantities of salt generated. Finally, it’s important to realise that this is a technology that is really only applicable close to the sea. For those that don’t have this luxury, other interventions will be required.”

The use of large-scale desalination plants is posing an increasing threat to the health of the seas, a recent report from the UN University found. For every litre of freshwater created from a conventional desalination plant, an average of 1.5 litres of brine is also made. Globally, desalination plants now discharge 142m cubic metres of highly salty brine every day, which is about 50% greater than previous estimates. In a year, that quantity would be enough to cover an area the size of Florida with 30cm of brine.

The report’s authors warned that the outflows of brine were depleting the dissolved oxygen in the surrounding seas, with damaging effects on marine life. They called for investment in promising new technologies which could reduce the amount of effluent that is wasted, by converting the metal byproducts – such as sodium, magnesium, lithium, calcium and potassium – to a useful form, which is currently uneconomic to do. They also suggested the saline byproducts could be used in fish farms, where saltier water can result in bigger fish, and in the irrigation of salt-tolerant crops.

Peak salt: is the desalination dream over for the Gulf states? Read more

Even with advances in desalination technology, there will still be drawbacks to its widespread use, not least issues of scaling up technology to the size of the water shortage problem. Virginia Newton-Lewis, senior policy analyst for water security at the charity WaterAid, says governments need to focus on myriad ways of providing the most fundamental service – clean water – to their populations, before becoming mired in what could be expensive and hi-tech desalination equipment. “What we need to see is universal provision of household drinking water to become a top political priority,” she says. “Lack of access to safe water supplies is often down to insufficient finance or political will to support basic services, rather than a physical absence of available water.”

Even in areas where water is physically in short supply, there are alternatives that should be explored as a matter of urgency. “Improved water management that prioritises household water supplies could have a huge impact, with very low economic costs,” she says. “It’s a matter of prioritising communities’ clean water supplies ahead of industry and agriculture. Desalination is expensive, causes pollution and has a number of limitations. Therefore, although it definitely has a role to play in certain areas, there are often much more appropriate solutions available.”

• Fiona Harvey is an environment correspondent for the Guardian

• This article is part of a series on possible solutions to some of the world’s most stubborn problems. What else should we cover? Email us at theupside@theguardian.com