Rainwater Harvesting Steps :: Collection using a Catchment System, Conveyance moves the water to a Storage Tank or Cistern

The Collection, Conveyance and Storage of Rainwater for Later Use
Commonly rainwater harvesting systems are constructed of three primary segments; (1) a collection method, (2) a conveyance component and (3) a storage facility. Rainwater harvesting collection, conveyance and storage systems can be incorporated into almost any existing site or building, although it is easier to incorporate a rainwater harvesting system into new construction.

(1) A collection or catchment system is generally a simple structure such as hard roofs and/or gutters that direct the rainwater through a conveyance component into storage. Roofs are ideal as catchment areas as they easily collect large volumes of rainwater. The amount and quality of rainwater collected from a catchment area depends upon the rain intensity, roof surface area and type of roofing material. For a 1,000 square foot roof, about 623 gallons can be collected, per inch of rainfall, regardless of pitch. Water quality from the roof catchment is a function of the type of material used on the roof, climate conditions, and the surrounding environment. If the collected rainwater is for potable use, select and use materials that will not leach toxins into the rainwater under normal or acid rain conditions. The roof material should be both non-toxic and inert.

(2) Conveyance components are required to transfer the rainwater from the roof catchment to storage. Conveyance is usually accomplished by connecting roof drains and piping from the catchment area (or roof top) to one or more downspouts that transport the rainwater through a filter system to storage in tanks for reuse or recharge.

A siphonic roof drainage system is one of the most effective technologies offered for capturing rainwater from a building roof top to aid in implementing rainwater harvesting. In a siphonic system several roof drain outlets can be connected to a single vertical discharge pipe. Fewer discharge points and no requirement for pitch in the piping means the rainwater can be easily routed horizontally below the roof to a storage tank, cistern, or retention pond.

One of the major benefits of designing a building with siphonic roof drainage and rainwater harvesting systems is reduced overall construction and facility operation costs. Additional benefits include reduced discharge of rainwater to lakes, streams, rivers and sanitary systems, and decreased dependence on municipal water supplies.

(3) Storage containers or cisterns for the harvested rainwater make stored rainwater available when needed. Depending on the space available these tanks can be constructed above grade, partly underground, or below grade. Various types of rainwater storage containers can be found in use. They include cylindrical ferrocement tanks (reinforced steel and concrete), mortar jars (large jar shaped vessels constructed from wire reinforced mortar), single and battery (interconnected) tanks made of either galvanized steel, concrete, ferrocement, fiberglass, or polyethylene, or they could be made of wood, metal, or earth. The polyethylene tanks are the most common, and easiest to clean and connect to the piping system. Storage tanks must be opaque to inhibit algae growth. They should be located as close to supply and demand points as possible to reduce the distance the water is conveyed.

Considerations for Fitting a Rainwater Collection System

Considerations for Fitting a Rainwater Collection System

The size of the storage container needed for a particular application is determined by the amount of water available for storage (a function of roof size and local average rainfall), the amount of water likely to be used (a function of the buildings occupancy and purpose), and the projected length of time without rain, aesthetics, and budget.

Before water is stored in a storage tank or cistern, and prior to use, it should be filtered to remove particles and debris. Filtration is a key element in the storage and use of harvested rainwater. Before entering the storage unit, rainwater should be filtered to remove leaf debris and other large particles. Upon leaving the cistern, the stored water is extracted from the cleanest part of the tank, just below the surface of the water, using a floating filter.