Annapolis, MD rainwater: 34,963 gallons off a roof
How much rain a roof in Annapolis, MD collects
34,963gallons a year
That is a 1,500 sq ft asphalt roof under Annapolis, MD's normal 44.0 inches of rain, about 795 gallons for every inch that falls.
In Annapolis, 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 Annapolis Naf station (2.2 mi away). Annapolis, MD ranks 18th wettest of the 23 cities covered in Maryland.
Month by month in Annapolis
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.84 | 2,257 | |
| Feb | 2.38 | 1,892 | |
| Mar | 3.80 | 3,020 | |
| Apr | 3.38 | 2,686 | 121 |
| May | 3.15 | 2,504 | 150 |
| Jun | 4.04 | 3,211 | 39 |
| Jul | 4.94 | 3,926 | |
| Aug | 4.27 | 3,394 | 10 |
| Sep | 5.14 | 4,085 | |
| Oct | 4.04 | 3,211 | 39 |
| Nov | 3.03 | 2,408 | |
| Dec | 2.98 | 2,369 |
Sep is the wettest month (5.14 in, 4,085 gal off the roof); Feb the driest (2.38 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
Which tank size is worth it in Annapolis
Best fit: one 55-gallon barrel, which delivers about 265 gallons to the garden in a normal year (74.1% 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 Annapolis's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 265 | 33,454 |
| 110 gal | 265 | 33,454 |
| 165 gal | 265 | 33,454 |
| 275 gal | 265 | 33,454 |
| 550 gal | 265 | 33,454 |
| 1,000 gal | 265 | 33,454 |
| 1,500 gal | 265 | 33,454 |
| 2,500 gal | 265 | 33,454 |
| 5,000 gal | 265 | 33,454 |
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