Water – the most fundamental of natural resources – is coming under pressure. And not just in the increasingly parched Middle East or North Africa. Even in Europe, about a third of the landmass and about 11 percent of the population suffers from water shortages.
Access to water is increasingly a source of conflict, and scientists say climate change is set to exacerbate water scarcity.
Making the most of the water we have is becoming essential to securing supply. And that might mean getting over squeamishness about wastewater.
"There is no doubt the potential for water recovery is very high," Steven Eisenreich, a geochemist at the University of Brussels told DW. "How big exactly, we don't yet know."
Normally, wastewater treatment involves cleaning, removing nutrients and discharging it back into rivers and lakes. But to make it suitable for immediate reuse, wastewater has to be treated even more thoroughly.
99 percent down the drain
This is already happening in countries including the US and Australia. Globally, about a third of treated wastewater is used for agricultural irrigation and 20 percent to irrigate landscapes such as lawns and golf courses.
But overall, very little wastewater is treated to this standard. In 2011, around 7 cubic kilometers of wastewater was reused across the world – less than 1 percent of total global water use. The rest of that potential remains untapped.
"Efficient use of wastewater reduces the amount of groundwater used for agriculture," Eisenreich said. "In addition, rivers become less polluted if less wastewater is returned to them. So it has advantages for both for quantity and quality of water."
The president of the World Water Council, Benedito Braga, also sees "recycling and reuse of wastewater as an important mechanism for tackling water shortages."
Wastewater to drink?
Braga considers taking this one step further, pointing to Namibia where treated wastewater is sometimes reused as drinking water. But in other parts of the word, public acceptance is seen as a barrier.
"The technology to turn wastewater into drinking water is there. But there's no backing for it," Eisenreich said. "And it's not foreseeable that this will exist in the future."
Agriculture is a different story. Particularly in regions suffering from water scarcity, wastewater can be a real alternative. Water-stressed Israel, for example, reuses 90 percent of its wastewater.
In Europe, there is a growing need for such solutions. Belgium, for instance, has severe water scarcity. Bulgaria also suffers from water shortages, but has made little use of its wastewater.
But public acceptance isn't the only barrier.
Complex and expensive
Reusing wastewater requires expensive modern treatment plants. Wastewater should, in theory, be treated in three steps before it's free of nutrients that could disrupt the water cycle. However, for direct reuse, wastewater must be treated even more thoroughly.
About 40 percent of Europe's wastewater treatment plants treat the wastewater in all three phases. This means, in theory, they have the capacity to treat wastewater thoroughly enough for the irrigation of green areas, for example.
"It is clear that for some time now European countries have been both collecting more wastewater and treating it to a higher quality," Caroline Whalley, project manager at the European Environment Agency, told DW.
Indeed, wastewater treatment has become a priority for the European Union since a European Commission blueprint in 2012.
Since then, many European countries have invested in wastewater infrastructure. In Greece, only 10 percent of wastewater was treated extensively in 2005. A decade later, 89 percent was receiving tertiary treatment. Countries like Romania have plans to follow Greece's lead.
Waste not, want not
Malta reuses around 90 percent of its wastewater. Yet there are no EU-wide standards. "There are already European countries that reuse water," Eisenreich said. "In doing so, they follow standards that are their own standards."
That could change. In 2016, the European Commission launched an initiative for minimum quality requirements . But the proposals are not yet binding and it's still up to each European member state to decide how much wastewater it reuses.
As the climate heats up, more and more countries may have to decide in favor of recycling. But worldwide, we're still a long way off.
Globally, 80 percent of wastewater is still returned to the environment without being treated at all – let alone to a level where it can be reused. We may not be able to afford such waste of a precious resource much longer.