Rainwater Harvesting – Water Conservation for Landscaping

What is rainwater harvesting?

Rainwater harvesting is the collection and storage of rainwater for later use, usually in landscape irrigation or household use such as washing laundry or cars, although with suitable equipment it can be used as drinking water.

Why harvest rainwater?

There are many reasons to harvest rainwater, some of them personal, such as a need for irrigation, and some of them more altruistic-conserving the finite water resources of the planet. And rainwater harvesting has been practiced for hundreds of years-at one time being the primary source of water for populations that did not have the benefit of living by a stream or river. But with the advent of reservoirs and piped municipal water, collecting rainwater for household use was no longer a popular option.

Today, however, the combination of a desire to reduce costs and to help to protect natural resources has led to the re-emergence of rainwater harvesting systems. But this time they are much more sophisticated than a simple rain barrel under the downspout.

What is needed in a rainwater harvesting system?

Large commercial enterprises might invest hundreds of thousands of dollars to collect run-off water from acres of roof space, but fortunately the systems needed for the average household do not require an investment on that scale.

A typical system might consist of a method for collecting the water from the roof and gutters, running through a filter to a storage cistern. This could be above or below ground and might be coupled with a pump if the storage tank is too low to rely on gravity to deliver to the point where it is needed.

Rainwater harvesting system components

Guttering and downspouts

The rain water running off the roof also collects a lot of undesirable elements such as leaves and debris from trees, feces from birds and animals as well as pollutants absorbed from the air. To eliminate as many as possible of these, the system should incorporate leaf guards and filters.

Filters

The type and size of filter to be used will depend on the size of the roof and the potential use of the system. One that is designed for potable water uses would need much more careful handling than one used purely for irrigation and non-potable household use. The minimum filtration would be a first flush fine filter that diverts about 5% of the water to ensure that any large contaminants are removed before the water is stored.

After that process, the stainless steel filter will remove the majority of the remaining contaminants.

Storage tanks

Once the water is in the storage vessel, any minor particulates will form a biologically active layer on the bottom and this will help in cleaning the water and reducing the sediment layer. As water is drawn from the tank it will pass through a further mechanical filter, usually in the form of a floating filter at the end of the suction hose. This ensures that water is drawn from an area remote from the bottom of the tank, reducing the likelihood of drawing up impurities and also lessening the risk of disturbance of the beneficial biological layer.