For decades, air-conditioning has been the answer to increasingly hotter summers in developed countries around the world, but now China is trying new ways of lowering temperatures in its overcrowded apartment complexes, and one such attempt is getting a lot of attention on social media.

Dubbed “rooftop rain,” the innovative urban cooling system has reportedly been implemented in Yuncheng, a city in northern China’s Shanxi Province, where several high-rise apartment buildings were fitted with rooftop misting systems that spray a fine mist of water into the air. This allegedly helps lower the temperature around the building by up to 8 degrees Celsius.

The rooftop rain system is based on a scientific principle called evaporative cooling. The high-pressure nozzles on top of the apartment buildings spray extremely fine droplets of water into the air, and as these droplets evaporate, they absorb heat from the surrounding air, cooling it, in a way that isn’t too different from how sweat cools down our bodies.

It’s important to note that the system is designed for very hot days, as the water sprayed from the top of the buildings needs to evaporate in contact with the hot air, instead of pouring down like rain on passers-by below. So maybe “rooftop mist” would have made a lot more sense.

This intriguing cooling system recently went viral on platforms like Reddit and Instagram, leaving millions of people wondering why it isn’t used on a wider scale, especially considering the heat wave ravaging Europe and North America right now. It’s a legitimate question, but there are a few things to consider.

While it does look (and probably feels) cool, the rooftop rain system is still a bit of an enigma. No one really knows how effective and efficient it really is. How much water does it require in order to cool the air on a large scale? Do the spray nozzles get clogged up by mineral deposits? What about the indoor temperatures in these buildings, does it drop significantly as well?

There are still a lot of things we don’t know, but China has reportedly installed rooftop rain systems in several cities, so there must be something to it.