Cambridge, MN rainwater: 23,574 gallons off a roof
Rainwater from a roof in Cambridge, MN
23,574gallons a year
That is a 1,500 sq ft asphalt roof under Cambridge, MN's normal 29.7 inches of rain, about 795 gallons for every inch that falls.
In Cambridge, MN a single barrel does most of the work. Storms come often enough that a small tank refills before it runs dry, and a bigger one would mostly sit full.
Rainfall: NOAA 1991-2020 climate normals, the Cambridge station (0.5 mi away). Cambridge, MN ranks 86th wettest of the 103 cities covered in Minnesota.
Month by month in Cambridge
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.74 | 588 | |
| Feb | 0.72 | 572 | |
| Mar | 1.38 | 1,097 | |
| Apr | 2.71 | 2,154 | 204 |
| May | 3.59 | 2,853 | 95 |
| Jun | 4.20 | 3,338 | 19 |
| Jul | 4.22 | 3,354 | 16 |
| Aug | 3.63 | 2,885 | 90 |
| Sep | 3.07 | 2,440 | 160 |
| Oct | 2.80 | 2,225 | 193 |
| Nov | 1.61 | 1,280 | |
| Dec | 0.99 | 787 |
Jul is the wettest month (4.22 in, 3,354 gal off the roof); Feb the driest (0.72 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
Barrel or cistern in Cambridge?
Best fit: one 55-gallon barrel, which delivers about 619 gallons to the garden in a normal year (79.7% of its need).
If you buy one, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Cambridge's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 619 | 22,040 |
| 110 gal | 619 | 22,040 |
| 165 gal | 619 | 22,040 |
| 275 gal | 619 | 22,040 |
| 550 gal | 619 | 22,040 |
| 1,000 gal | 619 | 22,040 |
| 1,500 gal | 619 | 22,040 |
| 2,500 gal | 619 | 22,040 |
| 5,000 gal | 619 | 22,040 |
Simulated storm by storm through a normal year using the station's count of days with 0.1 in or more of rain each month.
Is rainwater collection legal in Minnesota?
No statewide rainwater harvesting regulations; check county for local incentives
From the 2015 (Pacific Northwest National Laboratory report 24347); not yet re-checked against current law, so check with your state water agency before building anything large. Source