Frederick, MD rainwater: 34,590 gallons off a roof
How much rain a roof in Frederick, MD collects
34,590gallons a year
That is a 1,500 sq ft asphalt roof under Frederick, MD's normal 43.5 inches of rain, about 795 gallons for every inch that falls.
In Frederick, 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 Frederick Police Brks station (2.0 mi away). Frederick, MD ranks 20th wettest of the 23 cities covered in Maryland.
Month by month in Frederick
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.58 | 2,051 | |
| Feb | 2.95 | 2,345 | |
| Mar | 3.71 | 2,949 | |
| Apr | 3.55 | 2,822 | 100 |
| May | 3.99 | 3,171 | 45 |
| Jun | 4.26 | 3,386 | 11 |
| Jul | 3.90 | 3,100 | 56 |
| Aug | 2.89 | 2,297 | 182 |
| Sep | 5.80 | 4,610 | |
| Oct | 3.26 | 2,591 | 136 |
| Nov | 2.66 | 2,114 | |
| Dec | 3.97 | 3,155 |
Sep is the wettest month (5.80 in, 4,610 gal off the roof); Jan the driest (2.58 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 Frederick?
Best fit: one 55-gallon barrel, which delivers about 434 gallons to the garden in a normal year (81.9% 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 Frederick's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 434 | 33,016 |
| 110 gal | 434 | 33,016 |
| 165 gal | 434 | 33,016 |
| 275 gal | 434 | 33,016 |
| 550 gal | 434 | 33,016 |
| 1,000 gal | 434 | 33,016 |
| 1,500 gal | 434 | 33,016 |
| 2,500 gal | 434 | 33,016 |
| 5,000 gal | 434 | 33,016 |
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