In a study published in ACS Central Science, researchers at the National University of Singapore demonstrated a prototype that uses falling water droplets in a vertical tube to light up 12 LED bulbs — a modest but striking proof of concept.

Turning raindrops into voltage

The method taps into a well-known scientific principle: when materials touch, electric charge can be exchanged — just like static builds when a balloon rubs against skin. Water moving through certain surfaces can cause similar electrical activity through what's known as charge separation.

But unlike traditional hydropower, which relies on massive volumes of flowing water to spin turbines, this approach works at a much smaller and slower scale. That makes it especially appealing for urban areas where water flows may be limited.

Lead researcher Dr. Siowling Soh explains that their device mimics falling rain by shooting droplets through a metallic needle into the top of a tube, creating a ‘plug flow' — columns of water spaced by air. As the droplets move downward, they build up electrical charge which is collected by wires at either end of the tube.

A future where rooftops harvest rain energy?

The plug flow technique converted over 10% of the water's gravitational energy into electricity — a surprisingly efficient result for such a small setup. And since real raindrops fall faster than those used in the test, scientists believe the system could perform even better in the real world.

Unlike traditional hydropower stations, which require rivers and massive infrastructure, plug flow systems could be scaled down and fitted on rooftops, balconies, or anywhere rain falls. The research team believes this technology could offer a low-cost, low-maintenance alternative for harvesting clean energy in cities — one drop at a time.

As extreme weather becomes more frequent and the search for sustainable energy intensifies, perhaps future buildings will not just shelter us from rain — but turn it into power.