Find the best location
Walk around your home and look for a spot that has:
- A downspout from the roof
- A firm, level surface
- Easy access to your garden
- Space to reach the lid, filter, tap, and pump
- A safe route for overflow water
- No obstruction to doors, walkways, gas meters, or electrical equipment
Place the overflow away from your foundation and neighbouring properties. The City of Vancouver describes a rain barrel as a system that intercepts roof water from a downspout before it enters the storm drainage system.
Measure the available space
Measure:
- Maximum width
- Maximum depth
- Available height
- Distance from the downspout
- Distance to the garden
- Downspout shape and diameter
For a narrow side yard, a slim wall-style tank may work better than a round tank. One example is a 400-litre wall tank measuring about 1,200 mm wide, 400 mm deep, and 1,000 mm high (Rocky wall tank).
A standard round barrel may be easier for an open corner beside the house. BARR Plastics currently lists compact options such as a 310-litre round barrel and larger 520-litre square barrels (Square Rain Barrel).
Check how much water your roof can collect
Use this formula:
Roof area in m² × rainfall in mm × 0.8 to 0.9 = litres collected
For example:
50 m² of roof × 10 mm of rain × 0.85 = about 425 litres
Measure the horizontal roof footprint that drains into the selected downspout. You do not need to measure the sloped roof surface.
Literature: Rainwater Harvesting BEST PRACTICES GUIDEBOOK
Estimate your garden’s needs
A food garden may use roughly 20 to 40 litres per square metre each week during summer, depending on heat, soil, plants, and mulch. See how to keep your garden alive through the driest summer on record.
For a 20 m² garden:
- Lower estimate: 400 litres per week
- Higher estimate: 800 litres per week
A practical starting point would be:
| Garden or use | Suggested starting capacity |
| Patio plants and flower beds | 200-400 L |
| Small vegetable garden | 400-800 L |
| Average residential garden | 800-1,500 L |
| Large garden or some lawn watering | 2,000-5,000 L |
| Limited outdoor space | Slimline or underground tank |
These are planning ranges, not municipal requirements. Your roof area and watering demand should determine the final size.
Prepare a strong base
Water is heavy:
- 300 litres weighs about 300 kg
- 1,000 litres weighs about 1 tonne
- 3,000 litres weighs about 3 tonnes
Use a level concrete pad, compacted gravel base, or a manufacturer-approved platform. A raised barrel improves gravity pressure, but the stand must support the barrel’s full weight. Do not place a large tank on a deck without checking the structure.
Choose the system type
For a simple garden system, you normally need:
- Rain barrel or tank
- Downspout diverter
- Leaf and debris screen
- Secure lid
- Overflow hose
- Bottom tap
- Garden hose or watering can
For drip irrigation, you may also need a small pump, filter, pressure regulator, and timer. BARR Plastics lists systems ranging from compact rain barrels to large outdoor and underground tanks.
A basic outdoor barrel used only for garden watering is the simplest setup. A permanent system connected to household plumbing, toilets, municipal backup water, or pressurized building services may require treatment, backflow protection, plumbing compliance, and local approval.
Send me your available width, depth, height, approximate roof area, and garden size. I’ll estimate a suitable tank size and layout for the space.
