Rainwater Harvesting

What is it?
Special rainwater storage systems developed to harvest rain and use it for daily water needs. They are increasingly being applied in urban settings around the world to reduce water demand. Harvested rain can be used outdoors for irrigation, and indoors for toilet flushing, laundry and if filtered, as drinking water.

How does it work?
Rain harvesting systems capture, store, treat and deliver rain in both residential and commercial buildings. Simple harvesting systems consist of rain barrels that collect roof runoff for simple outdoor irrigation. More complex pumped systems involve large above ground or buried cisterns that store water collected from the roof. This water is then plumbed into the house, either as a replacement or supplement to the standard municipal water supply.

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A note:

Rainwater harvesting is common (or mandatory) in many parts of the world and is sometimes the only source of water (parts of Australia, Germany and California). In Ontario, rainwater harvesting is now permitted. In June 2006, the Ontario Building Code was amended allowing the use of rainwater using dual plumbing system inside a building.

The City of Toronto supports rainwater harvesting as part of its Wet Weather Flows Management Master Plan. The City is currently working on demonstration projects (at Exhibition Place and the Metro Zoo), with the longer term goal of wider implementation across the city. Toronto contains a national example of small scale residential rain harvesting in the Canadian Mortgage and Housing Corporation's demonstration Healthy House in Riverdale.

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Components of a Rain Harvesting System:

1. Collection Surface: The roof area draining to the downspouts.
2. Roof Washers: Usually a filter screen to catch the first flush of debris and pollutants from the downspouts before entering the storage cisterns.
3. Delivery System: The pipes that carry the water to the cistern - eaves troughs and downspouts.
4. Cistern/Tank: Storage tank for the water.
5. Filtration System: A chemical or organic filter to clean and treat the water - the extent of filtration depends on its end use
6. Distribution System: The pipes that deliver the water to the building. Can be the main water source or a parallel plumbing system (keeping drinkable and non-drinkable water separate).

What are the benefits?

• Reduces demand on municipal water supply.
• Allows for storage of seasonal rains for use in off peak times of droughts and urban water bans.
• Harvesting systems reduce erosion, property flooding and contamination by capturing the majority of urban runoff from a house.
• Reusing water saves considerable amounts of energy. 33% of the City of Toronto's electricity use in a year is spent on water pumping and treatment.

A few tips...

• A comprehensive rain harvesting system that is plumbed into a building requires expert advice for the design of the system and for assistance with seeking regulatory permission.
• When installing a rain harvesting system, ensure that there is suitable warning not to cross connect rain harvesting lines with indoor potable uses, and mark all pipes and faucets both indoor and outdoor as non-potable supplies not suitable for drinking.
• Connect your cistern or rain barrel to another stormwater management system like a soakaway pit to receive and infiltrate excess water when the system is full.

Costs:

• Reduces water charges from the municipal supply system
• Comprehensive systems are very expensive and need full professional design and consultation.

Maintenance:

Regular professional maintenance and inspections to ensure that the system is providing clean water and filtering properly is necessary. Cleaning the roof, eaves troughs, filters and monitoring water quality are ongoing requirements. If greywater is being recycled, further inspections will be needed.

Resources

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