Once water leaves the downspout, it needs somewhere to go. For rural properties, storage sizing and tank selection are the decisions with the most lasting consequences — a tank that freezes and cracks in January, or one that turns green with algae by August, undermines an otherwise sound collection system. This article covers the main tank types used in Canada, their practical trade-offs, and the basic calculations needed to size a system for a specific property.
Sizing the Storage Volume
The starting point is the intended use. A property relying on stored rainwater for garden irrigation only needs to bridge the gap between precipitation events. A property using rainwater as a primary household supplement needs a tank large enough to carry water through dry periods that can extend several weeks in summer in interior BC, southern Ontario, or the Prairies.
Irrigation Use
A vegetable garden of 50 m² in a dry July in Ontario might require 200–350 litres per week. A single 1,000-litre tank provides roughly three to five weeks of capacity between refills, depending on rainfall. For larger market gardens or small farm operations, multiple tanks linked in series — a common arrangement with IBC totes — allow incremental capacity expansion without large upfront costs.
Whole-Property Use
Sizing for household supply requires understanding your peak dry period. In most of Canada, a system sized to carry four to eight weeks of non-potable household water (toilet flushing, laundry) alongside the irrigation load is a reasonable starting target. For a family of four using rainwater for toilet flushing alone, that represents roughly 800–1,200 litres per week. An eight-week dry storage buffer requires 6,400–9,600 litres.
Tank Types
Polyethylene (Poly) Tanks
Rotationally-moulded polyethylene tanks are the most common above-ground storage solution for rural water in Canada. They are available from agricultural suppliers across the country in capacities from 200 litres to 25,000 litres. Food-grade high-density polyethylene (HDPE) tanks are suitable for storing rainwater intended for any use.
Key characteristics:
- UV-stabilized black or dark green tanks resist algae growth by blocking light — important for long-term water quality.
- Most poly tanks are not rated for burial unless specifically marketed as underground cisterns.
- Above-ground tanks must be drained before sustained freezing to prevent cracking at fittings. The tank body itself is flexible enough to handle some freeze pressure, but brass or steel fittings are not.
- Tanks should sit on a flat, stable base — compacted gravel or a concrete pad — to prevent stress concentrations on the base that can cause hairline cracking over time.
IBC Totes
Intermediate Bulk Containers (IBCs) are 1,000-litre cage-enclosed polyethylene containers originally used in food and chemical logistics. They have become a widely-used storage solution for rural rainwater systems because they are available used at low cost through farm supply dealers and online marketplaces.
Important considerations for IBC use in rainwater systems:
- Only totes that previously held food-grade products are appropriate for water storage. Totes that held industrial chemicals cannot be adequately cleaned for potable or irrigation use near edible crops.
- The clear HDPE inner container transmits light, promoting algae growth. Painting the exterior black, wrapping with shade cloth, or storing in a covered structure addresses this.
- IBC totes can be connected in series using their standard 2-inch threaded outlets, allowing simple capacity expansion.
- Like poly tanks, they should be drained at the outlet and disconnected from supply lines before winter.
Corrugated Steel Tanks
Corrugated steel rainwater tanks — lined internally with food-grade rubber or polyethylene — offer large capacities at moderate cost per litre. Common in Australian and New Zealand rural settings, they are less prevalent in Canada but are available through agricultural water supply specialists. Capacities typically range from 5,000 to 100,000 litres.
Corrugated steel tanks must be fully emptied and their liners inspected before winter. Any standing water in an uninsulated above-ground steel tank will freeze solid, potentially damaging the internal liner at its base.
Underground Cisterns
A buried cistern — concrete, fibreglass, or high-density polyethylene rated for underground installation — avoids the freeze-thaw problem entirely when installed below the local frost line. Frost depth in Canada ranges from roughly 60 cm in the southern Fraser Valley to over 200 cm in northern Alberta and Manitoba.
Underground cisterns maintain a more consistent water temperature, which slows biological activity. They do not require seasonal disconnection and can serve as the primary storage vessel for a year-round system.
The installation cost is higher than above-ground options — excavation, backfill, and proper inlet and outlet connections are required. Venting to prevent vacuum lock and an access hatch for inspection and cleaning are also necessary. Fibreglass cisterns rated for underground use are available from agricultural and water supply dealers in capacities from 1,000 to 45,000 litres.
Inlet and Outlet Design
The point where water enters the tank affects water quality inside it. A calmed inlet — one that reduces turbulence as water enters — prevents sediment already settled on the tank floor from being stirred up. A simple approach is to extend the inlet pipe to within 10 cm of the tank floor using a T-fitting that points horizontally rather than straight down.
The outlet used for irrigation or household supply should draw from a point 10–15 cm above the tank floor to avoid pulling settled sediment into the distribution system. A floating intake — a small intake fitting attached to a float — draws from the top of the stored water column, which is typically the clearest layer.
Overflow Management
Every tank needs an overflow outlet sized at least as large as the inlet pipe. Without a managed overflow, heavy rainfall can pressurize fittings or cause water to back up into the downspout system. The overflow should discharge to a point that does not direct water toward the foundation — a gravel-filled soakaway pit or a defined flow path away from the building.
Tank Maintenance
An annual inspection and cleaning cycle keeps stored water usable and extends tank life:
- Drain the tank completely once per year — typically in autumn before winter shutdown.
- Inspect the interior for sediment accumulation, biofilm, or visible algae growth.
- Rinse with clean water and drain again before refilling.
- Inspect all fittings, seals, and the overflow outlet for cracking or sediment blockage.
- Check gutter screens and the first-flush diverter as part of the same maintenance visit.
For more on treating water before it enters the tank and after it leaves, see the article on filtering rainwater for home and garden use. For the upstream collection system, refer to the guide on collecting rainwater from your roof.