Willmar, MN rainwater: 22,787 gallons off a roof
Willmar, MN: gallons off the roof each year
22,787gallons a year
That is a 1,500 sq ft asphalt roof under Willmar, MN's normal 28.7 inches of rain, about 795 gallons for every inch that falls.
In Willmar, 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 Willmar Wwtp station (1.4 mi away). Willmar, MN ranks 98th wettest of the 103 cities covered in Minnesota.
Month by month in Willmar
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.68 | 540 | |
| Feb | 0.67 | 533 | |
| Mar | 1.39 | 1,105 | |
| Apr | 2.63 | 2,090 | 214 |
| May | 3.33 | 2,647 | 127 |
| Jun | 4.79 | 3,807 | |
| Jul | 3.99 | 3,171 | 45 |
| Aug | 3.89 | 3,092 | 57 |
| Sep | 2.64 | 2,098 | 213 |
| Oct | 2.40 | 1,908 | 243 |
| Nov | 1.42 | 1,129 | |
| Dec | 0.84 | 668 |
Jun is the wettest month (4.79 in, 3,807 gal off the roof); Feb the driest (0.67 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 Willmar
Best fit: one 55-gallon barrel, which delivers about 741 gallons to the garden in a normal year (82.3% 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 Willmar's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 741 | 21,191 |
| 110 gal | 741 | 21,191 |
| 165 gal | 741 | 21,191 |
| 275 gal | 741 | 21,191 |
| 550 gal | 741 | 21,191 |
| 1,000 gal | 741 | 21,191 |
| 1,500 gal | 741 | 21,191 |
| 2,500 gal | 741 | 21,191 |
| 5,000 gal | 741 | 21,191 |
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