Westminster, MD rainwater: 37,062 gallons off a roof
Rainwater from a roof in Westminster, MD
37,062gallons a year
That is a 1,500 sq ft asphalt roof under Westminster, MD's normal 46.6 inches of rain, about 795 gallons for every inch that falls.
In Westminster, MD 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 Westminster 1.0 W station (1.0 mi away). Westminster, MD ranks 12th wettest of the 23 cities covered in Maryland.
Month by month in Westminster
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 3.36 | 2,671 | |
| Feb | 2.82 | 2,241 | |
| Mar | 4.08 | 3,243 | |
| Apr | 3.57 | 2,837 | 97 |
| May | 4.05 | 3,219 | 37 |
| Jun | 4.16 | 3,306 | 24 |
| Jul | 4.27 | 3,394 | 10 |
| Aug | 3.94 | 3,132 | 51 |
| Sep | 4.88 | 3,879 | |
| Oct | 4.33 | 3,442 | 2 |
| Nov | 3.34 | 2,655 | |
| Dec | 3.83 | 3,044 |
Sep is the wettest month (4.88 in, 3,879 gal off the roof); Feb the driest (2.82 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 Westminster?
Best fit: one 55-gallon barrel, which delivers about 171 gallons to the garden in a normal year (77.1% 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 Westminster's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 171 | 35,750 |
| 110 gal | 171 | 35,750 |
| 165 gal | 171 | 35,750 |
| 275 gal | 171 | 35,750 |
| 550 gal | 171 | 35,750 |
| 1,000 gal | 171 | 35,750 |
| 1,500 gal | 171 | 35,750 |
| 2,500 gal | 171 | 35,750 |
| 5,000 gal | 171 | 35,750 |
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 Maryland?
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