Canadian Rainwater Harvesting Potential Calculator (by City)

Quick answer

Rainwater harvesting is the water layer of the sovereign homestead — one more layer decentralized, alongside your own power and your own hashrate. How much you can collect is set almost entirely by two numbers: your roof footprint and your local annual precipitation. Across these 16 Canadian cities the ECCC Canadian Climate Normals 1981-2010 annual precipitation runs from about 262 mm in Whitehorse (a subarctic rain-shadow desert) to roughly 1,534 mm in St. John's. As a rule of thumb, every square metre of roof yields about 0.9 litres per year for each millimetre of rain, after collection losses — so a modest 50 m2 metal roof in Toronto (~831 mm) captures on the order of 39,000 litres a year.

Enter your roof footprint, roof type and city below to size your annual catch and a starting storage band. Free CSV/JSON under CC BY 4.0. Values are 30-year ECCC normals; a large share of prairie and northern precipitation falls as snow a winterized system will not catch — plan around the open-season rain fraction, and treat this as a planning reference, not potability or engineering advice.

Bitcoin taught us to run our own money; solar and storage let us run our own power; a rooftop and a tank let us run our own water. This calculator pairs your roof with the local rainfall normal to estimate what a rainwater-harvesting system could collect each year, then points you at a sensible storage band. It uses Environment & Climate Change Canada’s 30-year climate normals, so it reflects the long-run average — not any single wet or dry year.

Roof footprint (catchment area) Use the flat footprint (plan area) under the roof, not the sloped surface — rainfall is measured on the horizontal.Roof material (runoff coefficient)Standard collection-efficiency coefficients (splash, first-flush, minor losses): metal 0.95, asphalt shingle 0.90, flat gravel 0.80.City (annual precipitation)ECCC Canadian Climate Normals 1981-2010, annual total precipitation.

Download CSV Download JSON REST API →

Annual precipitation & rainwater potential by city

“Litres per 100 m² of roof / year” assumes a metal roof (0.95 runoff) and is a quick scaling anchor — multiply by your roof area in hundreds of m², and use 0.90 for shingle or 0.80 for flat gravel instead of 0.95.

City	Prov.	ECCC station	Annual precip (mm)	Litres / 100 m² / yr*	Confidence
St. John's	NL	St. John's Intl A	1,534	145,730	moderate
Halifax	NS	Halifax Stanfield Intl A	1,468	139,460	moderate
Quebec City	QC	Quebec / Jean Lesage Intl A	1,190	113,050	high
Vancouver	BC	Vancouver Intl A	1,189	112,955	high
Fredericton	NB	Fredericton A	1,078	102,410	high
Montreal	QC	Montreal–Trudeau Intl A	1,000	95,000	high
Ottawa	ON	Ottawa Macdonald-Cartier Intl A	920	87,400	high
Victoria	BC	Victoria Intl A	883	83,885	moderate
Toronto	ON	Toronto Pearson Intl A	831	78,945	high
Winnipeg	MB	Winnipeg Richardson Intl A	521	49,495	high
Edmonton	AB	Edmonton Intl A	477	45,315	high
Calgary	AB	Calgary Intl A	419	39,805	high
Regina	SK	Regina Intl A	390	37,050	high
Saskatoon	SK	Saskatoon Diefenbaker Intl A	365	34,675	high
Yellowknife	NT	Yellowknife A	289	27,455	high
Whitehorse	YT	Whitehorse A	262	24,890	high

St. John's: St. John's Intl A — among Canada's wettest cities (frequent rain plus heavy snow and drizzle). Integer value approximate; verify the exact ECCC station normal.

Halifax: Airport site (Stanfield) inland of the harbour; the coastal/downtown Citadel station differs. One of the wetter major cities — verify which station applies to your site.

Quebec City: ECCC 1981-2010 = 1189.7 mm at Quebec / Jean Lesage Intl A. Snowy climate — a large winter share (~300 cm snow).

Vancouver: ECCC 1981-2010 = 1189 mm at Vancouver Intl A (YVR, Richmond). Downtown and North-Shore stations are far wetter (Vancouver city ~1457, North Vancouver Capilano ~2522) — pick the station nearest your roof.

Fredericton: ECCC 1981-2010 at Fredericton A. Humid-continental Maritime valley; well-distributed rainfall with a snowy winter share.

Montreal: ECCC 1981-2010 ~1000 mm at Montreal–Trudeau Intl A, of which ~210 cm is snow. Reliable rainfall through the open season.

Ottawa: ECCC 1981-2010 at Ottawa Macdonald-Cartier Intl A. About a quarter of the annual total falls as snow.

Victoria: Victoria Intl A (Sidney / North Saanich) ~883 mm. The downtown Gonzales station is far drier (~705 mm); the Olympic rain shadow makes totals vary sharply over short distances — verify your microclimate.

Toronto: ECCC 1981-2010 at Toronto Pearson Intl A. The downtown lakeshore station is similar (~817 mm). Well-distributed year-round with a modest snow share.

Winnipeg: ECCC 1981-2010 at Winnipeg Richardson Intl A. Continental; roughly a quarter of the annual total arrives as snow.

Edmonton: ECCC 1981-2010 = 476.9 mm at Edmonton Intl A (366 mm rain + 111 mm snow-water). The city-centre (Blatchford) station is drier (~456 mm).

Calgary: ECCC 1981-2010 = 418.8 mm at Calgary Intl A (326 mm rain + 129 cm snow). High-elevation semi-arid prairie; a large share falls as snow, so a winterized system captures well under this figure.

Regina: ECCC 1981-2010 at Regina Intl A. Semi-arid continental; snow-heavy winter share.

Saskatoon: ECCC 1981-2010 at Saskatoon Diefenbaker Intl A. Semi-arid; roughly a third falls as snow — plan around the open-season rain fraction.

Yellowknife: ECCC 1981-2010 at Yellowknife A. Subarctic semi-arid; very dry, with much of the annual total falling as snow. Plan around the short open-water season.

Whitehorse: ECCC 1981-2010 at Whitehorse A. Subarctic rain-shadow desert — one of the driest cities in Canada; much of the total is snow, so a winterized (drained) system captures little of it.

Cold-climate reality. These figures are total precipitation and include snowfall water-equivalent. In prairie and northern cities a large fraction of the year’s water falls as snow. A gutter-and-tank system that is winterized (drained) each fall will not capture that winter precipitation, so your realistic collectable volume can be well below the annual number — plan around the open-season rain fraction, or design for snow-melt capture explicitly.

Non-potable, planning-only. Rainwater is non-potable without proper filtration and disinfection, and roof runoff carries debris, bird droppings and first-flush contaminants. This tool is a planning reference for garden and non-potable household use — it is not potability guidance and not an engineering design. Size real systems against your actual demand and local dry-spell length with a daily water-balance model, and follow your provincial/municipal plumbing and cross-connection codes.

The water layer of the sovereign homestead. Pair it with the Canadian solar resource (your power layer), the off-grid power components reference, and the Canadian heating-degree-days dataset (your heat layer) — then step back to the sovereignty hub. Climate data: Environment & Climate Change Canada, Canadian Climate Normals 1981-2010 (public domain). Normals are 30-year averages; verify the exact station value before design use.

Rainwater is the water layer of a resilient homestead. See how it stacks with solar power, reused miner heat, greenhouse food, and mesh comms in the Homestead Resilience hub.

Related products, repair, and setup paths

Last reviewed July 2, 2026.