Fergus Falls, MN rainwater: 21,356 gallons off a roof
Rainwater from a roof in Fergus Falls, MN
21,356gallons a year
That is a 1,500 sq ft asphalt roof under Fergus Falls, MN's normal 26.9 inches of rain, about 795 gallons for every inch that falls.
In Fergus Falls, 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 Fergus Falls station (2.0 mi away). Fergus Falls, MN ranks 100th wettest of the 103 cities covered in Minnesota.
Month by month in Fergus Falls
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.29 | 1,025 | |
| Feb | 0.83 | 660 | |
| Mar | 1.15 | 914 | |
| Apr | 2.00 | 1,590 | 293 |
| May | 3.86 | 3,068 | 61 |
| Jun | 4.35 | 3,457 | |
| Jul | 3.28 | 2,607 | 133 |
| Aug | 2.95 | 2,345 | 175 |
| Sep | 3.04 | 2,416 | 163 |
| Oct | 2.37 | 1,884 | 247 |
| Nov | 1.04 | 827 | |
| Dec | 0.71 | 564 |
Jun is the wettest month (4.35 in, 3,457 gal off the roof); Dec the driest (0.71 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 Fergus Falls?
Best fit: one 55-gallon barrel, which delivers about 868 gallons to the garden in a normal year (81.0% 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 Fergus Falls's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 868 | 19,663 |
| 110 gal | 898 | 19,633 |
| 165 gal | 898 | 19,633 |
| 275 gal | 898 | 19,633 |
| 550 gal | 898 | 19,633 |
| 1,000 gal | 898 | 19,633 |
| 1,500 gal | 898 | 19,633 |
| 2,500 gal | 898 | 19,633 |
| 5,000 gal | 898 | 19,633 |
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