The practice of capturing and storing rainwater for future use goes back thousands of years to when people first began farming the land. Their crops needed water during dry seasons so they quickly devised different ways to collect and store rainwater to use when it was not so abundant. These practices were used even prior to the Roman Empire. Today’s rainwater harvesting systems are much more sophisticated than those of the past, but they are used to achieve very similar goals.
Harvested rainwater is most commonly used as a non-potable water source for irrigation and/or flushing toilets and urinals. There are also more specialized uses related to specific industries and sites. The main objective of these more modern systems is to reduce the amount of fresh drinking water used for non-potable water requirements and reduce storm water runoff from entering the sewer systems and waterways.
Some of the benefits of rainwater harvesting include:
Helping to reduce flooding and sewer overflows by capturing and using water onsite.
Protect river and streams.
Reduce water and sewer bills.
Rainwater harvesting systems often use cisterns (storage tanks), pumps, filters, sensors, valves and piping to capture and redistribute the water. The catchment or collection area is typically a rooftop or paved parking area. When the catchment area is a rooftop, the water flows into the cistern via gutters or internal roof drains. If a paved parking area is the source of catchment, the water runs to the cistern via a catchment basin. Depending on the climate where the rainwater harvesting system is located, the cistern could be above grade or may need to be buried underground to avoid freezing.
Systems designed for the rainwater to be reused to flush toilets and urinals within a building will include mechanical filters and a form of water treatment, usually either ultraviolet or chemical, to prevent human health issues. Those designed for irrigation may include mechanical filtration but do not require other treatment. Today’s systems commonly utilize a float valve that automatically adds fresh water to the cistern before it gets empty to ensure there is never a water shortage. The amount of rainwater that can be captured by a rainwater harvesting system is determined by the amount of annual rainfall and size of the catchment area. In most cases, a rainwater harvesting systems can supply all of a facility’s non-potable water needs.
Overall, the current resurgence of this age old practice of recycling our rainwater has provided many environmental and economic benefits to our society.
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