What kind of facility is rainwater penetration masu?

Rainwater infiltration is different from ordinary rainwater, with holes in the bottom and wall surfaces, making it easier for rainwater to penetrate underground. By doing so, all rainwater does not flow into the river at once, and the infiltrated rain reaches the river slowly as groundwater or spring water. This reduces the flood damage​ and helps to grow trees and restore rich nature.
In Yokohama City, we subsidize a part of the installation cost when installing rainwater infiltration masu in residential land of houses and business establishments.

Rainwater infiltration