A Rain Water Collection System, or “RWCS” for short, is a system set in place to harness and maintain precipitation from a local environment. This can be for a variety of reasons, but ultimately the goal is to have usable water at the ready.
1. Catchment surface (roof)
Catchment surface – The RWCS usually starts with a roof. The roof is one of the main components in calculating the amount of rainwater that can be collected and is a key component of system size. The following formula can be used when calculating the approximate potential of collected rainwater.
Potential Rainwater collection (gal) = Catchment area (ft²) X Rainfall depth (in.) X 0.623
A 1,000 sq. ft. roof in a 1″ rain event has the potential to collect 623 gallons of rainwater
To calculate the annual potential of your RWCS you’ll need to know the annual average precipitation for your area and insert this number in rainfall depth. In the central Texas region, you can use 34″. This number is an average over the last 30 years. The above 1,000 sq. ft. the roof could potentially collect 21,182 gallons of FREE Rainwater annually! If you are not in this area use the precipitation map below.
The Conveyance sub-system consists of several details including gutters, covers, pre-filtration & trunkline. The trunkline can be dry or wet depending on a few factors such as size & complexity, property topography, economics & customer desire & esthetics. The above model depicts a wet trunk-line. Most high capacity systems (10K & higher) deploy a wet trunkline.
3. Storage tank & Pad
The Storage tank & pad can be the most visible and is the most expensive component in an RWCS. Tanks and cisterns can be made of many materials, sizes & shapes. The most common & economical tanks are Polyethylene or other plastic materials. Small (2,500 -5,000 gallons) poly tanks are very popular due their cost & ease of installation. Systems above 5,000 gallons are usually made from metal, fiberglass, concrete & steel and sometimes a combination of these materials. All tanks must have a tank pad to support the immense weight of the water; with water weighing-in at 8.43 lbs. or 3.785 kilograms (kg) at room temperature. A full 2,500 gallon tank weighs in at 21,075 or 10.5 tons. A 15,000 gallon tank weighs in at 126,450 or 63.2 tons. Water tanks need an adequate substructure to support its weight over the lifetime of the storage tank. All base pad structures must be designed to handle the dead weight of the water & tank and; must be designed and installed where rain & storm water are shed away. Base pads may be made of masonry and concrete materials. Most commercial tank pads are engineered and built using steel and concrete.
4. Distribution System
Distribution system – This sub-system can be as simple as a gravity fed hose or as sophisticated as a pressurized pump servicing multiple points of use.
5. Potable Components
Potable Components – This sub-system can converts the water stored in the storage tank into potable or drinking water; sometime referred to as Post filtration. This sub-system usually will consists of a sediment filter, charcoal filter & a UV disinfection system. Some of these systems also include ozonization, and or chlorination system. All of this systems should be configured to meet NSF-61 drinking water specifications.