In many parts of the world, getting a glass of clean water is as simple as turning on the tap. Cities use high-tech filters and UV lights to scrub out germs before the water ever reaches your house. However, for millions of people in places like Africa and South America, those systems aren’t an option.

While these regions might lack expensive infrastructure, they have plenty of sunlight. Eric Ryberg, a researcher at the University of Connecticut, and a team from Yale have found a way to use the Sun to create a better water filter. Their new device combines several old tricks into one small, solar-powered machine.

Finding a Safe Method For Clean Water

Cleaning water usually involves a few different approaches. You can boil it, but that takes a lot of fuel. You can use ceramic filters to catch bugs, or leave water in the Sun to let UV rays kill bacteria. The problem is that none of these work perfectly on their own. For example, viruses are tiny, tough, and can survive in a water bottle for 30 hours, even in direct sunlight.

“Many hands make light work in drinking water disinfection,” Ryberg said. “[It] really allows us to check a lot of boxes and provide water quality that allows people to feel dignified, no matter what resources they might have available to them.”

To fix the virus problem, Ryberg added something called a photosensitizer, a compound that reacts to light. It grabs energy from the Sun and uses it to turn oxygen into a “reactive” molecule that hunts down and kills viruses.

Real World Applications

The team used a common food dye called erythrosine as their secret weapon. Aside from killing germs, the dye does something else helpful: it fades as it works. When the water changes color, you know it’s safe to drink.

“Having multiple ways of disinfecting and treating the water is always better than having one, because while that prefiltration step is really effective for removing large organisms, like protozoa or worms, some smaller bacteria will slip through the filter,” Ryberg said. “Having technologies like pasteurization or solar disinfection are quite effective against bacteria. But those pesky viruses that don’t get inactivated quickly by those technologies, that’s where the photosensitization can really come in.”

In a field test in Guatemala, the system cleaned water in under an hour. When the Sun was at its brightest, it only took 28 minutes. Computer models showed that even in places with cloudy seasons, like Cape Town, South Africa, the system could provide 50 liters of clean water per person nearly every day of the year.

Right now, Ryberg is looking into using natural dyes like chlorophyll from plants to make the system even safer and easier to produce. “The ultimate goal is that we can transition to natural things that have a much lower toxicological concerns,” Ryberg added.