Laurel, MD rainwater: 37,761 gallons off a roof
Rainwater from a roof in Laurel, MD
37,761gallons a year
That is a 1,500 sq ft asphalt roof under Laurel, MD's normal 47.5 inches of rain, about 795 gallons for every inch that falls.
In Laurel, 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 Laurel 3 W station (2.2 mi away). Laurel, MD ranks 6th wettest of the 23 cities covered in Maryland.
Month by month in Laurel
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 3.46 | 2,750 | |
| Feb | 2.73 | 2,170 | |
| Mar | 4.20 | 3,338 | |
| Apr | 3.80 | 3,020 | 69 |
| May | 4.41 | 3,505 | |
| Jun | 4.38 | 3,481 | |
| Jul | 4.17 | 3,314 | 22 |
| Aug | 3.80 | 3,020 | 69 |
| Sep | 4.70 | 3,736 | |
| Oct | 4.41 | 3,505 | |
| Nov | 3.52 | 2,798 | |
| Dec | 3.93 | 3,124 |
Sep is the wettest month (4.70 in, 3,736 gal off the roof); Feb the driest (2.73 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 Laurel
Best fit: one 55-gallon barrel, which delivers about 125 gallons to the garden in a normal year (78.3% 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 Laurel's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 125 | 36,436 |
| 110 gal | 125 | 36,436 |
| 165 gal | 125 | 36,436 |
| 275 gal | 125 | 36,436 |
| 550 gal | 125 | 36,436 |
| 1,000 gal | 125 | 36,436 |
| 1,500 gal | 125 | 36,436 |
| 2,500 gal | 125 | 36,436 |
| 5,000 gal | 125 | 36,436 |
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