Alexandria, MN rainwater: 19,147 gallons off a roof
Rainwater from a roof in Alexandria, MN
19,147gallons a year
That is a 1,500 sq ft asphalt roof under Alexandria, MN's normal 24.1 inches of rain, about 795 gallons for every inch that falls.
In Alexandria, 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 Alexandria Muni Ap station (1.1 mi away). Alexandria, MN ranks 103rd wettest of the 103 cities covered in Minnesota.
Month by month in Alexandria
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.38 | 302 | |
| Feb | 0.41 | 326 | |
| Mar | 1.00 | 795 | |
| Apr | 2.04 | 1,621 | 288 |
| May | 3.05 | 2,424 | 162 |
| Jun | 3.72 | 2,957 | 79 |
| Jul | 4.00 | 3,179 | 44 |
| Aug | 3.46 | 2,750 | 111 |
| Sep | 2.63 | 2,090 | 214 |
| Oct | 2.21 | 1,757 | 267 |
| Nov | 0.83 | 660 | |
| Dec | 0.36 | 286 |
Jul is the wettest month (4.00 in, 3,179 gal off the roof); Dec the driest (0.36 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
What size rain barrel for Alexandria
Best fit: one 55-gallon barrel, which delivers about 939 gallons to the garden in a normal year (80.6% 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 Alexandria's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 939 | 17,503 |
| 110 gal | 966 | 17,476 |
| 165 gal | 966 | 17,476 |
| 275 gal | 966 | 17,476 |
| 550 gal | 966 | 17,476 |
| 1,000 gal | 966 | 17,476 |
| 1,500 gal | 966 | 17,476 |
| 2,500 gal | 966 | 17,476 |
| 5,000 gal | 966 | 17,476 |
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