Harvesting Rainwater

Water is a precious resource essential to all life.

For millennia, people experiencing regular or periodic lack of water developed ingenious methods to harvest and store every drop of rainwater they could. With changing climate patterns, depletion of water tables, and water restrictions due to unprecedented periods of heat and drought, many BC residents now realize that an abundant water supply is not assured and are thinking about harvesting and conserving this precious resource.

What is Rainwater Harvesting?

Rainwater harvesting is another way to manage stormwater runoff with the added benefit of being able to put that excess water to use at a later date when water is in shorter supply. Harvesting rainwater typically involves collecting and storing rainwater that would otherwise run off a roof or other impermeable surface. During storms, this diversion of runoff can help prevent flooding and erosion. On the flip side, during dry periods, using the stored water can take pressure off our natural freshwater resources – lakes, streams, and groundwater that may be depleted.

How does rainwater harvesting benefit salmon?

It diverts stormwater runoff from impermeable surfaces which could otherwise contribute to habitat damage from flooding and erosion where spawning salmon lay their eggs and young salmon rear.

Using harvested rainwater takes off pressure on natural water resources during periods of drought, such as late summer and early fall when salmon need water in streams to migrate.

Stormwater runoff often contains pollutants that negatively impact the ecosystem, diverting this water can prevent pollution from entering sensitive environments.

Check out the runoff management article for more information on common contaminants, and other nature-based solutions to capture runoff: Nature-based Solutions to Manage Stormwater Runoff.

Here are a few more benefits of harvesting rainwater:
  • Reduce pollutants flowing into lakes, streams, oceans, and groundwater– redirecting and reducing stormwater by harvesting rainwater can minimize the pollutant loads that enter sensitive ecosystems. .
  • Depending on the setup, a system can contribute to groundwater recharge – using a system that filters and redirects water into the ground can recharge aquifers.
There are two main methods of rainwater harvesting

Rooftop rainwater harvesting involves collecting rainwater from the roofs of buildings and houses using gutters, pipes, filters, and tanks or rain barrels. The collected water can be used for various household needs, such as washing, gardening, and even cooking or drinking (depending on the type of roof and ability to purify). Rooftop rainwater harvesting can also recharge groundwater aquifers by diverting the excess water to wells, boreholes, or recharge pits. Here is a schematic of a typical rooftop rainwater harvesting:

Surface runoff harvesting involves collecting rainwater that flows over the ground using swales, ponds, rain gardens, reservoirs, in-ground tanks, and percolation through penetrable surfaces, like sand, gravel, and permeable pavements. Collected water can be used for irrigation and watering livestock. It can also recharge groundwater aquifers when water is directed to infiltration basins, trenches, or percolation tanks instead.

There is no one correct way to harvest rainwater. It depends upon the system's scale, budget, and purpose; however, the costs can vary widely depending on the solutions employed.

Rain Harvesting for Homeowners

Rooftop rain harvesting is the most common and least costly approach for household purposes. Rain barrels, the cost of which are subsidized by many local governments, receive rainwater from a downspout attached to the roof's gutter and provide easily accessible water for the garden and other outdoor purposes, typically having a faucet or hose attachment at the bottom. Multiple barrels can be interconnected via pipes to store a significant amount of water.

For small-scale harvesting for use in the garden, you can even DIY in an afternoon with items from a hardware store, see this example of step-by-step instructions from instructables.com.

For households that do not have a municipal water source or those with significant water needs for garden plots and livestock, a more elaborate system may be required.  There are large storage tanks that can hold thousands of gallons of water, which can be placed above or below ground. The tank can be connected to a pump and a filtration system to deliver clean water to different parts of the house or garden.

For large-scale harvesting and when you plan to use the water in your home, including for drinking water, it is best to seek the help of professionals.

Wondering how much you can harvest?

In this post about rainwater harvest ideas on morningchores.com, there is a rainwater harvest calculator. Simply put in the catchment area (the width and length (ft) of your roof you intend to capture water from) and the amount of rainfall (in) expected and it will tell you how many gallons you would receive.

If you wish to calculate it yourself (or prefer metric measurements), for every square metre of roof catchment area and millimetre of rainfall, one Litre of water will be produced. Based on that you can use the following formula will calculate your expected total:

Catchment area (m2) x annual local average rainfall (mm) = ____L

So, for a 10m x 10m (or 100m2) roof in Nanoose, which receives an average annual rainfall of 1086mm, there would be 108,600L (or 108.6m3) of rainwater. Note that the maximum efficiency of a typical harvest system would be between 75-80% of that total due to evaporation, periods of overflow etc.

Learn about rainwater harvesting in BC

In addition to, or instead of rooftop harvesting systems, simple surface runoff harvesting techniques, such as rain gardens and swales, are increasingly popular techniques to capture and filter rainwater.  These do not usually supply a readily available source of water for household use but do contribute to groundwater replenishment and natural purification, making water available to plants within the immediate vicinity while also serving to remove pollutants that could otherwise be swept into waterways.

Rainwater harvesting is an ancient and sustainable practice that can help conserve water, save money, improve plant health, and provide an emergency water supply, all of which improves the climate resiliency of our families and communities. By collecting and storing rainwater for later use, we can use a precious natural resource that would otherwise go to waste.

Additional Resources

For further information on rainwater harvesting, including ways to establish your own system, try these sites and resources:

Water Harvesting Basics (wateruseItwisely.com)

Water Harvesting - Definition, Importance, Methods, Limitations (geeksforgeeks.org)

23 Awesome DIY Rainwater Harvesting Systems You Can Build at Home (morningchores.com)

Rainwater Harvesting: A Beginner’s Guide (treehugger.com)

Beginner’s Guide to Rainwater Harvesting (familyhandyman.com)

Smith, J. (2010). Rainwater harvesting: Benefits and challenges. Journal of Environmental Science, 12(3), 45-56.

Photo credits: Ed Leszczynskl on Unsplash, Eiko Jones, Photo licensed under CC BY-NC, Photo licensed under CC BY-NC-ND Paul de Greeff, Nicole Christiansen, Illustration by Holly Sullivan

Plant a Rain Garden

A rain garden is a great example of a nature-based solution to reduce stormwater runoff from your property.

Rain gardens are attractive landscaping features that are specially designed to treat runoff and allow water to infiltrate the soil and recharge ground water.

How does a rain garden benefit salmon?

A rain garden treats runoff from around your property to reduce the amount of pollutants that enter streams and coastal areas, keeping these habitats healthy for salmon.

Rain gardens encourage what would otherwise be runoff to soak in and replenish groundwater. This helps prevent erosion during wet times and helps maintain stream baseflows during dry times to help migrating salmon.

How rain gardens work

With a rain garden, runoff from roofs and other impermeable areas around the property are directed to a sunken area where water can pond and move through a mix of mulch and constructed organic soils planted with appropriate native species. Rain gardens allow natural bio-remediation processes of microorganisms, plants, and soils to take place, which prevents contaminants making it to stream and shore habitats.

The group 12,000 Rain Gardens in Puget Sound shares a wealth of knowledge on building rain gardens that is specifically relevant to the Pacific Northwest. See their comprehensive guide on building a rain garden, and watch their video demonstration linked below.

Also check out the Rain Gardens for Headwaters: Online Design Symposium hosted by Kyle Armstrong with Peninsula Streams & Shorelines. Kyle is joined by speakers Deborah Jones, Cougar Creek Streamkeepers, Kristen Miskelly, Satinflower Nurseries, Brianne Tenk, Stormwater Management Specialist, City of Victoria, and Scott Murdoch, Landscape Architect, Murdoch De Greeff Inc. You will learn about lessons learned and “do’s and don’ts” from constructing rain garden designs, the importance and benefits of utilizing native plants in rain gardens, green stormwater infrastructure, and much more!

As mentioned in the talk by Brianne Tenk, The City of Victoria has an incentive program for managing rainwater sustainably, such as receiving credits and rebates for incorporating pervious pavers, rain barrels and rain gardens on your properties! To learn more about the City of Victoria’s Rainwater Rewards Program for rainwater harvesting and management, see here!

Additional Resources

Check out our partner Peninsula Streams Society's blog about three Rain Garden Demonstration Sites they have built at urban schools in the Capital Region. This project has built storm and drought resilience into local watersheds! Within the post are a number of helpful and informative links.

For professional assistance with designing and building a rain garden, search for landscape architect firms through the BC Society of Landscape Architects.

Photo credit: Maria Cantanzaro and Paul de Greeff

Permeable Paving

A source of pollution entering waterways comes from stormwater runoff from around our homes. In particular, a paved driveway, which may have car oil and road residues, delivers contaminated runoff to gutters and drains that directly connect with aquatic environments.

Fortunately, there are options, such as permeable pavers, gravel or grass grid systems, and specialty concrete mixes, that allow storm water to filter through to the soils below.

Using these alternatives has a number of environmental benefits, including lower pollutant loads entering water ways, reduced erosion and flooding from flashy storm runoff and increased groundwater recharge. Additionally, less radiant heat is retained by these alternative systems compared to traditional concrete. This will reduce heat pollution that contributes to urban heat island effect.

Depending on the type of solution selected, installation methods and costs will vary. Typically, pavers are placed on a level bed that allows infiltration and spaces between are back-filled with fine gravel. Detailed installation guides and summaries of different options can be found online (here too).

Learn more about the how cars can cause water pollution and ways to reduce the impact, here.

Photo credit: Toinane on Unsplash, Nicole Christiansen, Kyla Sheehan, and Paul de Greeff