California Homeowner Collects Rainwater in Underground System

California restrictions on using potable water for lawn irrigation, gardening, clothes washing and showering can be strict. To bypass the restrictions, a Half Moon Bay, Calif., homeowner used non-potable water from an underground storm water harvesting system for irrigation.

During rainstorms, water from the roof is diverted to the gutter and downspout system. Instead of hitting a downspout splash guard and traveling to the storm sewer, the water is delivered to an underground chamber. The chamber stores the water until it is needed to supplement the home’s irrigation system. A pump and piping system then delivers the water to sprinkler heads.

Invisible Structures Inc. designed the Rainstore3 system to be installed under the driveway of the house, making a normally unusable space functional. The system is a series of vertically stacked modular units connecting cylinders on a grid. The chambers are 94% efficient, meaning only 6% of the volume is lost to the product and the rest can be used for water storage. 

The product is completely wrapped by geotextile fabric and an impermeable membrane liner. The only openings are for water inflow, pump and pipe outflow, air intake, and a maintenance port. 

The system is composed of 80 Rainstore3 units, stacked five units high (50 cm), in a four-by-four stack configuration (4 by 4 meters). The product is rated for H-20 loading and can handle residential vehicle weights. The system can hold 1,987 gal of water for irrigation.