In some parts of the world, harvesting rain is the only way to get water. About a decade ago, researchers from Canada Mortgage and Housing Corp. (CMHC) started looking at the benefits of using rain as a water source. They discovered that rainwater harvesting (RWH) systems in North America were not only rare, but in some municipalities they were prohibited.

Since then, CMHC and several governments and universities have worked to develop guidelines for RWH systems, and to change the building codes to allow rainwater harvesting.

In the City of Toronto, managing stormwater costs millions of dollars each year. A lot of the city’s surface has been paved over during the last 100 years, so there has been more and more stormwater to deal with and it is overloading aging sewer systems. This creates overflowing rivers and creeks, flooded basements and polluted beaches along Lake Ontario. Toronto’s water pumping and treatment facilities use 33 per cent of the city’s electricity in a year.

The city has already passed a bylaw that makes it mandatory for homeowners to disconnect their downspouts from direct connections to the sewer system. The idea is that rainwater will drain onto lawns and gardens and put less strain on the city infrastructure. RWH systems are the next step, taking that rainwater and using it outdoors to irrigate the lawn and garden. The most basic of these systems is a simple rain barrel that collects the water, which can then be used to water the plants and the lawn.

In many Canadian jurisdictions, rainwater can now also be used indoors for toilet flushing and laundry. The most extensive - and expensive - RWH systems have filters to create drinking water. CMHC says collecting and using rainwater is undergoing a modern-day revival, with RWH systems installed in several "green home" pilot projects, including one in the Riverdale area of Toronto. The federal housing agency found that one of the major barriers for RWH systems in Canada was the lack of information about how to design, install and manage them. That led to the creation of the Guidelines for Residential Rainwater Harvesting Systems as well as a training workshop that is now available.

There are six components to an RWH, says Riversides, an information service developed by the City of Toronto, Environment Canada and the Toronto and Region Conservation Authority. The collection surface is usually the roof of a building that drains to the downspouts. There is a filter screen that removes leaves and other debris before the water travels down to a storage cistern or tank. Then there is a chemical or organic filter to clean and treat the water, depending on its end use. Finally, there is a distribution system to carry the water to the building. This can be the main water source for the house or a line that is completely separate from the drinking water.

Riversides says a comprehensive system that is plumbed into a building requires expert advice for the design of the system, and for "assistance with seeking regulatory permission." Some other points to considers, says Riversides, is to ensure there is a warning not to cross-connect rain harvesting lines with indoor potable water lines. All the pipes and faucets that have non-potable water must be clearly marked.

The cistern or rain barrel should also have measures in place to deal with overflow water when the system is full, such as a "soakaway" pit, says Riversides. The guidelines include a section on overflow provisions.

The guidelines say: "Other considerations include how the design, installation and management of RWH systems can affect the quality of water saved and the quality of rainwater harvested, as well as cold weather suitability of the system."

A CMHC research paper (the project manager is Cate Soroczan) says: "The development of residential rainwater harvesting guidelines supports a water-conserving approach that will help improve the overall sustainability of housing and communities." It says the guidelines help to ensure a consistent, national approach to the design, installation, performance and management of RWH systems. It will also help in the development of commercially available systems and make both municipalities and homeowners more aware of the benefits of these systems.

"Though the requirements for the design and construction of RWH systems resides with the building authority having jurisdiction in any given area, the development of these guidelines will serve to promote a common approach to RWH systems, which can help facilitate more widespread acceptance and uptake of this technology," says CMHC.

The Guidelines for Residential Rainwater Harvesting Systems book is available here.

Guidelines specific to Ontario are available here.

Guidelines for Alberta are available here.

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