Thousands of cities around the world could power themselves entirely using solar panels on reservoirs, reports The Verge. It’s a relatively simple way to generate renewable energy locally while conserving water. New research, published in the journal Nature Sustainability, shows what potential cities can realize thanks to this new technology.

Researchers found that 6,256 cities in 124 countries around the world could theoretically meet all of their electricity needs by using solar panels placed atop nearby water reservoirs. To do this, they only need to cover about 30% of the water surface with floating solar panels.

Researchers analyzed 114,555 reservoirs around the world using multiple databases and then modeled potential electricity production using realistic climate data.

And since all these floating arrays will block enough sunlight to reduce evaporation, the researchers also predict significant water savings. In total, the panels will save about as much water as 300 million people could use annually (or about 106 cubic kilometers per year).

However, developers will still need to evaluate each reservoir to limit any negative side effects. For example, if you cover too much of a pond with solar panels, it can lead to a decrease in the amount of oxygen in the water, which can harm the fish. Construction on artificial reservoirs, rather than on natural reservoirs, may be a less harmful option, the publication notes.

The study found that the greatest potential for floating power plants is concentrated in places where there are already many communities living near reservoirs. These are, as a rule, small settlements of up to 50,000 people. Only 15% of the studied cities with a population of more than 1 million people would be able to meet all their electricity demand exclusively using floating solar power plants.