Rain Harvesting - Bypass Overflow
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Underground Water Collection System
RAIN HARVESTING or RAIN CAPTURE is becoming increasingly popular for landscape irrigation due in part to recent improvements in drip irrigation technology. Darco manufactures underground fiberglass rain water storage tanks.
A one inch rain on a 2000 square foot roof generates over 1000 gallons of free water. Arid western states such as New Mexico and Arizona support and promote Rain Harvesting and Drip Irrigation which returns moisture to the soil at slow absorbable rates with minimal evaporative loss.
Always design your storage system with a high volume cap to divert excess rain water that can not be stored fast enough during a downpour. Also consider a tank cap to release any excess water when the storage system is completely full. Both the bypass and overflow must be directed away from the tank and discharged where it will not cause erosion or lead to structural building damage. (See Illustration #1)
We do not recommend that you drink or bathe in rainwater unless it has been treated to your local Health Department standards. Rainwater should rightfully be used in a way that returns the moisture to the earth near the location where it fell, such as through outside landscape irrigation or a septic system leach field.
Roof water generally carries leaves, dust, bugs, bird excrement, and a variety of other undesirable elements into any rain capture storage system. Screening or filtering the water before it fills the storage tank is desirable provided the filter has the capacity to process the rain as fast as it falls. This may be difficult to do in the case of a "cloud burst". A high volume bypass should be designed into any rain water collection system for such event.
Illustration #2 depicts our rain capture system with a simple inlet basket screen and an upstream bypass.
A shallow upstream concrete silt interceptor will greatly reduce the amount of sludge collected in the bottom of the primary storage tank. Accumulated silt in the bottom must be removed every few years by vacuum truck.