Fairmont, MN rainwater: 26,594 gallons off a roof
How much rain a roof in Fairmont, MN collects
26,594gallons a year
That is a 1,500 sq ft asphalt roof under Fairmont, MN's normal 33.5 inches of rain, about 795 gallons for every inch that falls.
In Fairmont, 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 Fairmont station (0.1 mi away). Fairmont, MN ranks 32nd wettest of the 103 cities covered in Minnesota.
Month by month in Fairmont
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.85 | 676 | |
| Feb | 1.16 | 922 | |
| Mar | 1.93 | 1,534 | |
| Apr | 3.53 | 2,806 | 102 |
| May | 4.58 | 3,640 | |
| Jun | 5.02 | 3,990 | |
| Jul | 3.88 | 3,084 | 59 |
| Aug | 3.79 | 3,012 | 70 |
| Sep | 3.44 | 2,734 | 113 |
| Oct | 2.32 | 1,844 | 253 |
| Nov | 1.58 | 1,256 | |
| Dec | 1.38 | 1,097 |
Jun is the wettest month (5.02 in, 3,990 gal off the roof); Jan the driest (0.85 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
Which tank size is worth it in Fairmont
Best fit: one 55-gallon barrel, which delivers about 490 gallons to the garden in a normal year (82.1% of its need).
If you set one up, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Fairmont's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 490 | 25,174 |
| 110 gal | 497 | 25,167 |
| 165 gal | 497 | 25,167 |
| 275 gal | 497 | 25,167 |
| 550 gal | 497 | 25,167 |
| 1,000 gal | 497 | 25,167 |
| 1,500 gal | 497 | 25,167 |
| 2,500 gal | 497 | 25,167 |
| 5,000 gal | 497 | 25,167 |
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