A team from the University of Toronto is investigating how solar-powered, UV LED lights can zap the pathogens in harvested rainwater, so that households no longer have to spend a huge part of their income on expensive bottled water.
According to Unicef, turning on the tap to pour a glass of clean drinking water is still little more than a pipe dream for more than 2 billion people across the world. In Mexico, the issue is particularly acute, with around 57% of the population still lacking easy access to clean drinking water, due to a mixture of an ageing infrastructure and population growth, as well as extreme heat, droughts and floods caused by climate change.
The research is being led by the Centre for Global Engineering (CGEN), a multidisciplinary research institute at the university, where engineering researchers and students are working to solve some of the world’s most pressing problems and challenges, from food insecurity and sanitation, to energy poverty and safe housing.
But the project is not just about engineering, says Karlye Wong, the PhD student leading the research. “Water is so interconnected with so many other things. That’s why the team also includes geographers, economists and sociologists, as well as engineers,” she says.
“It’s part technology, part user adoption,” says Wong. “And looking at what we can do to make people want to engage with and use different systems to make use of such a precious natural resource.”
So alongside Prof Ron Hofmann, a recognised global expert on water treatment technologies, and principal investigator at the University of Toronto’s Drinking Water Research Group, the team has also been able to call on the experience of sociologist Yu Chen to examine aspects such as technology adoption and community water initiatives. “By including the social sciences too, we are able to do something that has even broader impact,” says Wong.
Typically, when harvesting rainwater for household use, it’s initially gathered from rooftops and gutters. It then runs through a first flush, to remove larger pieces of debris, before flowing into a secondary tank and then the building’s plumbing system. But to be drinkable, the bugs and the microbes in the rainwater also need to be killed.
One of the most common ways of doing this is adding chlorine to the water. “The idea of adding chemicals to drinking water is unpopular with many people,” says Wong. “And the smell and the taste of the water can also be off putting.”
Other systems use UV light to purify the water. At appropriate wavelengths, UV light can make microbes and pathogens in the water inactive and unable to spread diseases, leaving the water safe to drink.
However, these systems have proved expensive to run and maintain, with bulbs that need regular changing. A third way is using solar-powered UV LEDs, which are far less energy intensive than conventional lamps, says Wong. And introducing flow sensors, which remotely turn the lights on and off, makes them even more affordable to run.
Through regular trips to Mexico, the University of Toronto researchers are gathering evidence to establish a blueprint for the best ways to install and maintain the systems. So far they have found the technology to be effective, easy to use and widely accepted by users, which include schools and households, Wong says. “We want to make sure UV LEDs are sustainable in the long term.”
The team are working closely with Isla Urbana, a Mexican social enterprise that is installing rainwater harvesting systems across local communities. “There are a lot of synergies with our work and that of Isla Urbana,” says Amy Bilton, director of CGEN and a professor of mechanical engineering. “It’s an organisation that really values research.”
Other joint projects include looking at ways to reduce the carbon emissions associated with supplying water, as well as knowledge sharing between Indigenous communities in Mexico and Canada.
Rainwater harvesting can also help with climate resilience, says Bilton, as many areas of Mexico are prone to heavy rainfall. The harvesting systems can help to divert some of this water, and help provide drinking water, rather than causing flooding or being channelled into storm drains.
At the moment, she says, most of these rainwater technologies are developed in the global north, where the conditions in which they need to operate can be very different from the global south.
“Changing this mindset is another important part of our work, and we want to nudge the water industry to start investing in technologies that are better suited for the settings where they are often needed most,” says Wong.
“Countries like India, Indonesia and the Philippines could all benefit from new ways of turning rain into drinking water.”
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