Salisbury, MD rainwater: 38,159 gallons off a roof
Rainwater from a roof in Salisbury, MD
38,159gallons a year
That is a 1,500 sq ft asphalt roof under Salisbury, MD's normal 48.0 inches of rain, about 795 gallons for every inch that falls.
In Salisbury, 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 Salisbury station (0.7 mi away). Salisbury, MD ranks 3rd wettest of the 23 cities covered in Maryland.
Month by month in Salisbury
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 3.58 | 2,845 | |
| Feb | 3.19 | 2,535 | |
| Mar | 4.20 | 3,338 | |
| Apr | 3.57 | 2,837 | 97 |
| May | 3.72 | 2,957 | 79 |
| Jun | 4.32 | 3,434 | 4 |
| Jul | 4.83 | 3,839 | |
| Aug | 5.26 | 4,181 | |
| Sep | 4.33 | 3,442 | 2 |
| Oct | 3.93 | 3,124 | 52 |
| Nov | 3.41 | 2,710 | |
| Dec | 3.67 | 2,917 |
Aug is the wettest month (5.26 in, 4,181 gal off the roof); Feb the driest (3.19 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 Salisbury?
Best fit: one 55-gallon barrel, which delivers about 187 gallons to the garden in a normal year (79.8% 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 Salisbury's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 187 | 36,802 |
| 110 gal | 187 | 36,802 |
| 165 gal | 187 | 36,802 |
| 275 gal | 187 | 36,802 |
| 550 gal | 187 | 36,802 |
| 1,000 gal | 187 | 36,802 |
| 1,500 gal | 187 | 36,802 |
| 2,500 gal | 187 | 36,802 |
| 5,000 gal | 187 | 36,802 |
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