Harvesting Rain Water

Many of us are aware that running the tap while rinsing or washing dishes, brushing our teeth, or  over watering the lawn is wasteful.  Many Canadians already conserve water by being careful with over running the taps, but what are other ways for saving fresh water?

Environment Canada reports that municipal water systems leak up to a quarter of our demand during water distribution. While this infrastructure weakens, since 1980, our water use has increased by  almost 27% (Eco-Research, University of Victoria).

Concurrently, we have enough renewable fresh water fall as rain to meet our annual needs.  Capturing, filtering and storing this water is not a new concept.  For example, the Governor General’s residence has an original wooden cistern intact in it’s attic.  Rainwater harvesting is more than sustainable and eco-friendly, it also lessens the municipal load and saves us money.

However, Health Canada has not detailed out their issues regarding safety, which results in challenges of building a truly sustainable water system.  

Rain Water

What is rainwater harvesting? Rainwater harvesting involves the collection, storage and treatment of rainwater for uses such as watering plants and garden, for use in toilets as well as laundry.  Depending on the final use, the degree of treatment may vary.

How do you capture the water?  Collecting water from hard surfaces, such as the roof, is easier than from vegetable roofs or from the surrounding flat property.  
Asphalt shingles are not as desirable for plant and sanitary uses because of the presence of tar that contaminates the water collected.  Lawn water can also be collected by  using drainage piping that can use the earth for filtering.

Treatment and cleaning:  Other than removing large items like leaves and twigs, no special cleaning is needed if the water will be used for swimming pools, gardening, laundry and toilets.  However, ultraviolet [UV] treatment is a safety measure for killing any bacteria.  If the water is intended for direct contact with people (or pets), as in showers and sinks, additional treatment will be necessary.

Re-using Water

Water can also be collected from baths, laundry and sinks (not including the kitchen sinks) and are classed as ‘greywater’.  Water from kitchen waste is known as ‘wastewater’ and should be disposed of in the same manner as toilet waste, which is called ‘blackwater’ [sewage].

Greywater can be collected and reused in a myriad of ways:

1) draining the shower or sink, directly into the tank of the toilet;

2) directing greywater from laundry and showers to irrigate plants and garden; or

3) reprocessing/treating greywater for all uses except drinking.

Where the quantity of greywater is not sufficient to meet the full demand of toilets and laundry, potable water is needed. Protection is taken against possible cross contamination between pipes.

Cleaning and Treating Rain Water and Greywater

There are three stages to cleaning water: screening, filtering and disinfecting.

Screening:  With rain water collection, all unwanted solids such as twigs, are removed.  No additional treatment or cleaning is needed if rainwater will be used for exterior landscaping or swimming pools.
Filtering:  Sand filtering can be used to sufficiently filter greywater for toilet use. Adding chlorine would make the water appear clean but offers little other benefit.
Disinfecting: The use of UV lighting kills bacteria making the water better suited for use in laundry.  However, UV utilizes electricity, making this process less sustainable and eco-friendly. 

Storage:  Exterior tanks are most desirable when buried with protection against heaving when the ground water table is higher than the water level inside the tank.  Protection against freezing is possible without insulation if buried below the local frost level (4 ft for this part of the region) or insulation can be added above the tank.  For interior tanks, tight sealing is important to prevent any humidity from building-up inside the home.  Plastic tanks are more practical because of their weight and cost.  Periodic water circulation (either mechanically or by flushing) is vital to avoid long-term storage of water, to avoid bacterial growth. All tanks also require an overflow.


Health Canada states, “Although effective treatment can produce domestic reclaimed water that is virtually free of disease-causing microorganisms, a small number of pathogenic organisms may still be present and pose some risk, such as accidental cross-connections between the reclaimed system and the drinking water system.”
At this time, Ontario and Alberta have guidelines and British Columbia has enacted a reclaimed water standard for a variety of applications, including for toilet flushing and agriculture. The Ontario Building Code states that rainwater only needs to be free of solids for use in toilets. The National Building Code requires that any piping for non-potable use be separate from the standard piping for regular potable water, and labelled as such.

The desire to reduce demand on city water infrastructure by municipalities, and the general move to more sustainable eco-living, will eventually make these technologies available to the average homeowner.


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