Hermantown, MN rainwater: 24,583 gallons off a roof
Rainwater from a roof in Hermantown, MN
24,583gallons a year
That is a 1,500 sq ft asphalt roof under Hermantown, MN's normal 30.9 inches of rain, about 795 gallons for every inch that falls.
In Hermantown, 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 Duluth Nws station (2.8 mi away). Hermantown, MN ranks 74th wettest of the 103 cities covered in Minnesota.
Month by month in Hermantown
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.92 | 731 | |
| Feb | 0.95 | 755 | |
| Mar | 1.35 | 1,073 | |
| Apr | 2.50 | 1,987 | 231 |
| May | 3.20 | 2,543 | 143 |
| Jun | 4.49 | 3,569 | |
| Jul | 4.13 | 3,283 | 27 |
| Aug | 3.55 | 2,822 | 100 |
| Sep | 3.50 | 2,782 | 106 |
| Oct | 3.02 | 2,400 | 166 |
| Nov | 1.98 | 1,574 | |
| Dec | 1.34 | 1,065 |
Jun is the wettest month (4.49 in, 3,569 gal off the roof); Jan the driest (0.92 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 Hermantown?
Best fit: one 55-gallon barrel, which delivers about 612 gallons to the garden in a normal year (79.2% 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 Hermantown's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 612 | 22,981 |
| 110 gal | 612 | 22,981 |
| 165 gal | 612 | 22,981 |
| 275 gal | 612 | 22,981 |
| 550 gal | 612 | 22,981 |
| 1,000 gal | 612 | 22,981 |
| 1,500 gal | 612 | 22,981 |
| 2,500 gal | 612 | 22,981 |
| 5,000 gal | 612 | 22,981 |
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