Rainwater Harvesting

Rain Water Harvesting

Each citizen in Canada uses an average of 329 liters of drinking water per day (Statistics Canada 2004). 90 liters are used for toilet flushing alone, which along with garden irrigation can be considered a waste of drinking water.

Configuration of a Rain Water Harvesting System

Rain Water Harvesting SystemIn general a rain water harvesting system consists of the following components:

Cistern

Filter

In-house water treatment system

Plumbing

Rain water running off the roof is channeled through a filter and collected in a rain water storage tank. Depending on the space available the tank can be installed inside the house or outside underground. Tanks used inside the house are usually made of polyethylene. Plastic or concrete cisterns can be installed underground in the back yard. A calmed inlet allows any pollutants in the rainwater to settle at the bottom of the tank. A connection to a canal or drainage pit prevents overflow when the cistern is full.

A suction pump supplies the water collected in the storage tank at the places of use. This requires a separate plumbing system, usually made out of plastic. An automatic filling level detection and a device for replenishment of drinking water assure continuous water supply when the storage tank is empty.

System Size

Since the cost of the storage tank accounts for up to 50% of the system price it is essential to determine the required storage tank size. The cistern size depends on the roof area available for rain water collection and the required amount of water. For example, a roof area of 120 m2 with an annual precipitation of 537mm would require a storage tank of approximately 3000 l. Based on a completely filled cistern with a daily usage from a four person household of 360 l (for toilet flushing only) the stored water reserves would last for about 11 days.

Applications for Rain Water Harvesting

While a system for garden irrigation can be installed any time, systems for the house and garden require a special plumbing system and are therefore primarily of interest in new developments or renovations. In addition to garden irrigation and toilet flushing, rain water can also be used for laundry. Rain water leaves significantly less lime scale deposits in washing machines and less laundry detergent is needed.