Greenbelt, MD rainwater: 34,987 gallons off a roof
Rainwater from a roof in Greenbelt, MD
34,987gallons a year
That is a 1,500 sq ft asphalt roof under Greenbelt, MD's normal 44.0 inches of rain, about 795 gallons for every inch that falls.
In Greenbelt, 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 Beltsville station (3.5 mi away). Greenbelt, MD ranks 16th wettest of the 23 cities covered in Maryland.
Month by month in Greenbelt
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.87 | 2,281 | |
| Feb | 2.40 | 1,908 | |
| Mar | 3.72 | 2,957 | |
| Apr | 3.28 | 2,607 | 133 |
| May | 4.27 | 3,394 | 10 |
| Jun | 4.23 | 3,362 | 15 |
| Jul | 4.51 | 3,585 | |
| Aug | 3.88 | 3,084 | 59 |
| Sep | 4.42 | 3,513 | |
| Oct | 4.04 | 3,211 | 39 |
| Nov | 2.92 | 2,321 | |
| Dec | 3.48 | 2,766 |
Jul is the wettest month (4.51 in, 3,585 gal off the roof); Feb the driest (2.40 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 Greenbelt
Best fit: one 55-gallon barrel, which delivers about 200 gallons to the garden in a normal year (78.3% 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 Greenbelt's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 200 | 33,648 |
| 110 gal | 200 | 33,648 |
| 165 gal | 200 | 33,648 |
| 275 gal | 200 | 33,648 |
| 550 gal | 200 | 33,648 |
| 1,000 gal | 200 | 33,648 |
| 1,500 gal | 200 | 33,648 |
| 2,500 gal | 200 | 33,648 |
| 5,000 gal | 200 | 33,648 |
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