A residential rain water harvesting system was placed under a large patio in back yard. Thunder Mountain designed the retention tank, which can be used for irrigation and emergency water source in case of fire. The retention tank, when full, overflows into a secondary detention tank where the water can infiltrate and recharge the water table. Rainwater enters the tank through pervious pavers and filtered water from roof downspouts. The tanks can collect and infiltrate as much as 60,000 gallons of rain water per year.