Marshall, MN rainwater: 22,970 gallons off a roof
Marshall, MN: gallons off the roof each year
22,970gallons a year
That is a 1,500 sq ft asphalt roof under Marshall, MN's normal 28.9 inches of rain, about 795 gallons for every inch that falls.
In Marshall, 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 Marshall station (1.6 mi away). Marshall, MN ranks 93rd wettest of the 103 cities covered in Minnesota.
Month by month in Marshall
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.86 | 684 | |
| Feb | 0.87 | 691 | |
| Mar | 1.60 | 1,272 | |
| Apr | 2.79 | 2,218 | 194 |
| May | 3.66 | 2,909 | 86 |
| Jun | 4.10 | 3,259 | 31 |
| Jul | 3.78 | 3,004 | 71 |
| Aug | 3.61 | 2,869 | 92 |
| Sep | 3.06 | 2,432 | 161 |
| Oct | 2.29 | 1,820 | 257 |
| Nov | 1.26 | 1,001 | |
| Dec | 1.02 | 811 |
Jun is the wettest month (4.10 in, 3,259 gal off the roof); Jan the driest (0.86 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 Marshall
Best fit: one 55-gallon barrel, which delivers about 726 gallons to the garden in a normal year (81.3% 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 Marshall's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 726 | 21,359 |
| 110 gal | 726 | 21,359 |
| 165 gal | 726 | 21,359 |
| 275 gal | 726 | 21,359 |
| 550 gal | 726 | 21,359 |
| 1,000 gal | 726 | 21,359 |
| 1,500 gal | 726 | 21,359 |
| 2,500 gal | 726 | 21,359 |
| 5,000 gal | 726 | 21,359 |
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