Flowsand is sharp paving sand to use with regular pavement. The sand is coated with a water-conducting additive which gives the sand a capillary function. The sand can quickly suck water from the street surface into the junctions and then slowly release it into the soil. As a result, much less water is drained to the sewer and much more remains available for the city, to replenish the groundwater level or cool the city.
Flowsand is deliberately designed as a slow system to prevent water pressure in the soil beneath the pavement. It should therefore not be confused with permeable road surfaces that are aimed at rapidly draining water. Instead, Flowsand takes a little bit off of every shower. Light showers provide about 90% of the yearly precipitation volume, and it rains half of the days. The expectation is that, by absorbing little amounts of each shower, Flowsand can take in more than 50% of the annual precipitation.
The setup at The Green Village serves for further validation and research.