Sourcing the Rain: Install a Rainwater Catchment System in Your Home

Rain falling on roof

Rainwater harvesting is one strategy to reduce domestic water use. Harvesting rainwater can lead us to dozens of other practices that bring us into greater sustainability. Growing plants that shade and insulate windows reduces energy use; increasing home food production reduces demand for wasteful water use in industrial fields. Above all, rainwater harvesting increases quality of life: ours, and that of life worldwide.

In arid climates and places with salty irrigation, rainwater flushes salts and chemicals out, allowing for long-term health and soil vitality.

On any house lot, there are three potential sources for harvesting the rain: Direct rainfall, street harvesting, and roof harvesting.

Design landscape to welcome the rain

The easiest rainwater source is that which falls on the yard. Proper placement of plants, trees, and water sources can turn the site into a water efficient system. Shape the surface of the soil to slow down runoff, raise paths and patios, and sink all planting areas to capture the flow. Choose plants—primarily natives—that can absorb and hold water in their root systems, or pass it down to the water table. This way, rainwater doesn’t run off into the street, where it would be swept away with motor oil, into the sewer system or discharged directly into a local waterway.

Harvest runoff—curbcuts and bioswales

The second source of rainwater is the street. Streets aren’t flat; they are typically graded so that water flows to the curb, down the block to a gutter and into the storm drain. In some cities storm drains are connected to the sewer treatment plant, and heavy rains cause the sewer plant to overflow raw and partially treated sewer into lakes or rivers. Other cities connect storm drains to underground creeks, and the polluted water runs straight into the lake or nearby river. By cutting curbs and digging sunken basins into the “right-of way” or “parking strip” area of the sidewalk, you can turn street rainwater from a problem to a resource. Diverted rain that falls on streets can nourish plants, protect creeks, and contribute to cleaner cities.

The third source of rainwater is the roof. Even in areas with low rainfall there’s enormous potential for harvesting rainwater. A 1,000 square foot house can collect about 2300 litres per inch of rain! So in an average year with 23 inches of rain in Toronto, that small roof could collect 1,380,000 litres.

The rain catchment system

A water catchment system for roof rainwater is simple, and can store water for outdoor irrigation.

  • Gutters: Roof water gathers in the gutters and runs to a pipe towards the tank.
  • “First Flush”: The first rain of the year is the dirtiest as it cleans the roof. This water is directed away from the tank in a “first flush system” and the subsequent water continues to the tank.
  • Screen: The rainwater goes through a screen to remove leaves and debris, and then funnels into the top of the covered tank.
  • Storage: The tank is dark, to prevent algae from growing, and screened, to prevent mosquitoes from entering.
  • Irrigation:A hose attachment is located near the bottom for irrigation.

Rainbarrels are a popular way to begin rainwater harvesting, especially in urban areas; they’re low cost, and can be installed along houses, under decks, or in other unused spaces.

There’s a huge range of options for cisterns—large single storage tanks. They can be made from plastic, ferrocement, metal, or fiberglass,ranging in size from 50 gallons to tens of thousands of gallons.

Indoor use

Ceramic drinking water filter: This highly-effective, passive filter removes pollutants and pathogens including viruses from drinking water. These systems can reduce or eliminate use of municipal or well water during the rainy season, when outdoor irrigation is unnecessary. Most household rainwater systems use a pump and pressure tank to pressurize water. EPA and other research has shown that rainwater harvested using a “first flush” system and protected from light is safe to use for bathing and other household use. Filtering only the small amount of water used for drinking with passive filters such as the ceramic filter shown at left, or with slow sand filters, greatly reduces system cost, and offers an affordable solution for people needing clean drinking water.

Article originally published on Greywater Action


Assess your situation

If it is not for financial reasons why are you installing a water tank? Here are some reasons:

  • Do your part for water conservation
  • Be able to water your garden with some independence from water restrictions
  • Make rainwater available for drinking in your home – see this info (PDF)
  • Use rainwater in the laundry and toilet

What size water tank should I choose?

Get the biggest tank you can fit in your garden. As a rule of thumb, about 25,000 litres of storage is considered enough for a small family to be nearly self sufficient for normal domestic usage. The storage size will vary according to local rainfall. Dry areas would require more storage, wet areas less.

A cheap and simple solution

You can get started with rainwater collection by installing diverters in downpipes and filling a large garbage bin, but with this system there is no “first flush diverter” to remove impurities from the first quantity of rainwater from the roof. Water can be distributed from the bin/tank using gravity or a small pump.

Types of water tanks

  • Cyclindrical tanks – either plastic or galvanized iron are often the cheapest, but they require a lot of space.
  • Rectangular and other narrow tanks – either plastic or galvanized iron can fit under eaves and in narrow spaces next to fences. However, they are lower volume and more expensive.
  • Collapsible bladder systems can be installed under houses between existing stumps. This is the most expensive option.

Other considerations

  • If you use tank water for showering, be aware of the difficulties matching different water pressures. The mains pressure is often higher than what a pump can produce and the mains pressure can stop the tank water from coming through the pipes.
  • There are strict government regulations concerning the connection of mains water and tank water systems. The intention is to prevent tank water systems possibly contaminating the mains system. A licenced plumber must install this type of connection. These regulations don’t apply if the systems are plumbed seperately.
  • The ability to fill tanks also depends on the roof catchment area you have. If the catchment area is too small you may never fill large tanks. This can be calculated from the average rainfall events for your location and the roof area.
  • In city areas use a green plumber. Many urban plumbers are not acquainted with installing and connecting rainwater tanks, systems and pumps.


  • Larger tanks will often need to be installed in back yards using a large crane to lift it over the house roof or back fence (if there is rear access).
  • Check with the tank retailer for the cost of using a crane. Some retailers will offer a free crane install for tanks over a specific size, below that size you may have to pay separately for the cost of the crane hire (which could be $300 to $500).
  • Tanks can be partially buried – up to a third the height of the tank is usually possible. If you bury tanks deeper than that without taking special measures they can “pop out” of the ground if the tank is empty and the water table rises. A drain system around a buried tank site with a sump and water pump installed could avoid this happening and enable the tank to be more fully or completely buried. This type of installation should be done professionally.
  • Ensure that every tank has a valve installed at its outlet. This will allow you to isolate the tank quickly and easily to work on the pipe system. Also, if you damage the pipe outlet system you can shut the valve to prevent the entire contents of the tank being lost.
  • Tanks can be installed under decking if the decking support structure is designed to leave space underneath to accommodate the tank.
  • All tanks must have an overflow connection to stormwater (or perhaps another lower tank).
  • Choose your water tank pump carefully – it is very important to calculate the pressure and flow required to get the appropriate performance.

Article originally published on Greenlivingpedia

image: Martin Cathrae via Compfight (Creative Commons BY-SA)
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