For centuries, people have collected rainwater for drinking, washing and irrigation purposes. With the advent of municipal water treatment, rainwater collection became less popular in urbanized centres, though water storage cisterns can still be found in old farmhouses across Canada. But recently, rainwater harvesting has experienced an increase in popularity in countries around the globe as a result of droughts, water shortages and the rising costs of drinking water and stormwater infrastructure. Canada, too, is experiencing an increase in rainwater harvesting for lawn and garden irrigation, and many municipalities have begun to offer rebates for rain barrels. But larger, more sophisticated systems that capture, store, treat and redirect greater quantities of rainwater for other uses are still relatively new.
Rainwater harvesting systems use rainwater collected from the roof and should not be confused with systems that recycle treated wastewater or greywater (water from baths, showers and laundry). Rainwater that has touched the ground is generally not collected, as it can be contaminated with leaked automobile fluids, road salt, pet droppings, pesticides, fertilizers and dirt.
Some municipal planning codes now permit the use of non-potable (not safe to drink) water for toilet flushing and subsurface irrigation, while others permit the use of rainwater for laundry washing. Codes and bylaws will set out requirements for the appropriate materials to be used, sizing, supports, protection and marking, as well as the steps needed to ensure that non-potable water does not mix with potable (drinkable) water from the municipality or your well. Before installing a rainwater harvesting system, it is important to check with your municipality first to ensure the design and installation of your system will be in compliance with local regulations.
Depending on what you wish to use your rainwater for, your system can range from very small and simple to large and complex, with the cost varying accordingly. A general rule of thumb is that your system will cost $1/litre so that smaller 2000 litre systems will cost around $2,000. The first step will be to determine the quantity of water you will need for your intended purposes, the size of your roof catchment area and the amount of rainfall your area typically receives in a year. Based on this information, a rainwater harvesting system designer can work with you to determine how much rain you can realistically collect, how big of a cistern you will need and what you can use this water for. Cisterns have come a long way from the simple rain barrel. They come in different sizes (50 – 200,000 L), shapes (rectangular, square, cylindrical, bag) and materials (concrete, fibreglass, plastic, steel, wood) and can be installed above or below ground. Cisterns and related components should be insulated or emptied to avoid freezing in the winter months.
While there are currently very few regulations for rainwater quality, a rainwater harvesting system can include some level of treatment to stop the system from clogging up and to help ensure good water quality. Gutter filters, screens and systems that divert the “first flush” of rainwater are used to reduce the amount of leaf litter, insects, pollens, dust and other pollutants that can collect on roofs and get into the rainwater system. Screens are also used on access openings on the cistern to keep out insects, rodents, etc. Stored rainwater can also be treated with cartridge or membrane filters and then disinfected with chlorine or ultraviolet light prior to use. Check with your local health agency to determine what treatment (if any) is required in your jurisdiction. Once installed, it will be necessary to maintain your system as per the manufacturer’s instructions to ensure optimal performance. It is important to inspect and clean out gutters, check filters and check for leaks at least once a year.
In most cases, you will need a pump to deliver the treated rainwater from the cistern to the garden or your house. It is important to ensure that all plumbing and piping for the distribution system are adequately sized and installed for optimal flow. Consideration must be given to redirecting excess rain to a soakaway pit or infiltration trench to prevent the cistern from overflowing during heavy storm periods. Consider having your system designed, installed and commissioned by a professional.
Rainwater harvesting systems offer an effective way to reduce your water bills, use plant-friendly water in your garden and reduce your demands on local water infrastructure. To learn more about rainwater harvesting systems, visit CMHC’s website (www.cmhc.ca) to view the consumer guide to rainwater harvesting, or call 1-800-668-2642 to request a copy of the publication.
For over 65 years, Canada Mortgage and Housing Corporation (CMHC) has been Canada’s national housing agency, and a source of objective, reliable housing information.
Published: June 6, 2013