There are three main ways to use stored rainwater.
1. Gravity drain systems for landscape irrigation
2. Pumped systems for landscape irrigation
3. Pumped systems for indoor use
The rainwater catchment system consists of these basic components:
Gutters: Rainwater drains off the roof into gutters and is piped to the storage tank. Gutters are often screened to prevent leaves from entering the gutters.
Pre-filter/screen: The rainwater goes through a screen to remove leaves and debris. Screens can be placed on the gutters, integrated into the gutter downspouts, or be placed on a pipe which drains from multiple downspouts. It is best to place the screen before the first flush as the screen will keep the first flush from clogging.
"First Flush": The water from the first few minutes of each rain event is the dirtiest as it picks up dirt and dust which tends to accumulate on the roof. This water is directed away from the tank in a "first flush diverter" and the subsequent water continues to the tank. Usually 1 gallon is diverted per 100 square feet of catchment area.
Storage: The tank is dark to prevent algae from growing, and screened to prevent mosquitoes from entering.
Pumps and filters: If the rainwater is to be used indoors, or through a drip irrigation system, the rainwater is pumped and filtered to it's final destination (there are gravity based drip irrigation options as well).
1. In urban areas, rainbarrels are a popular way to begin harvesting rainwater. They can be installed along sides of garages, property lines, under decks, and in other unused spaces.
2.Cisterns, or water storage tanks, offer a large capacity for storing rainwater, ranging from hundreds to tens of thousands of gallons. They can be made from plastic, ferrocement, metal, or fiberglass. Cisterns can be placed either above ground or buried below ground.
3. A pillow tank (or bladder tank) is an option for small lots where a large above ground or below ground tanks isn't an option. Pillow tanks can be placed under decks or below the house in crawl spaces.
The existing house downspout is redirected to the rainbarrel or tank. The barrel has an overflow to send rainwater out when it is full, and a hose connection near the bottom. When the water is needed, open a valve and rainwater flows out the garden hose. Multiple barrels can be connected together, providing as much storage as there is space for.
Rainwater can be connected from rainbarrels or a cistern to a drip irrigation system. If the drip irrigation is tubing is at a lower elevation than the cistern, non-pressure compensating drip tubing can be used to apply the rainwater to the landscape using only gravity and manual valves. If automation is required, an irrigation controller can turn on a rainwater pump which supplies water to the landscape through drip irrigation tubing.
Rainwater can be used indoors to flush toilets and wash clothes in the laundry machine. Using rainwater indoors makes a lot of sense in urban areas that have long dry summers and wet winters where large storage cisterns would be required to store irrigation water for use during the summer, and irrigation is not required in the winter. Using rainwater indoors requires extra filtration using sediment, carbon and UV light filters. Read more about filtering rainwater here.