Rainwater Harvesting

This is a subject many of our clients ask about. Although lack of rainfall has not been an issue yet this year, normally by now we’d be thinking about the municipal or well water we will need to satisfy the gardens that we West Coasters love.

Canada ranks 28th out of 29 countries for per capita water consumption*. I suspect that throughout the Gulf Islands and Vancouver Island, people are more aware than the average Canadian about water conservation, but that doesn’t mean we use any less! The average British Columbian uses approximately 490 litres of water per day**. Here’s a neat, but by no means comprehensive, test to assess your water footprint – http://goblue.zerofootprint.net/?language=en

So what can we do to save water? Most people know that low-flow fixtures are widely available, economical and are mandatory in all new construction. Obviously just changing our habits to conserve will make a big difference, and planting native and drought-tolerant plants will reduce the water required. But when we do want to irrigate, why not use harvested rainwater?

Collecting rainwater for potable use is a growing trend, but since filtration becomes more involved, I’ll concentrate here on irrigation. Our climate is perfect for collecting water throughout the winter for use during the dry summer months.

First, you need a suitable roof collection material – the most common is metal; concrete or slate tiles are also good. Asphalt shingles can be used but are harder to keep clean. A new cedar roof is not considered a good collection surface, but aged shingles that have leached most of their toxins should be ok. Shingles that contain moss inhibitors are not suitable for use on plants, especially veggies!

Charts showing the amount of rainfall collected from a roof surface can be found at Rainwater Connection – see link below.

There are lots of variables, and defining your needs is the first step. A collection system can be as simple as barrels at the bottom of your downspouts to an elaborate automated system with buried storage tanks and zoned irrigation. It can be a diy project using off the shelf products (with a little knowledge and a lot of hard work) to a professionally designed and installed layout. You can gravity feed with a garden hose, or pump from storage tanks through a pressurized system.

A few basics to bear in mind if you are attacking this yourself – make sure your collection vessel is adequately screened to prevent mosquito larvae growth, and that your above-ground tanks are secure in case of earthquake. Make sure your gutters are cleaned regularly. A leaf guard on the downspout is a good idea, and a “nice-to-have” is a gauge to tell you how much water is in your tank. As with any construction project, up-front planning will yield more satisfying results and save you time, money and frustration along the way.

The links below show a wide variety of systems, and lots of useful information for designing your project:





http://www.robertkourik.com/books/drip.html – This is my go-to book on diy irrigation, and it’s entertaining to read on a rainy day when you’re not out in the garden!

*among OECD countries – Organization for Economic Cooperation and Development

** BC Living Water Smart http://www.livingwatersmart.ca/watersmart/at_home.html

Note: Wilco Construction Ltd. does not necessarily endorse specific companies or products mentioned above.