Concord, NH rainwater: 33,342 gallons off a roof

Concord, NH: gallons off the roof each year

33,342gallons a year

That is a 1,500 sq ft asphalt roof under Concord, NH's normal 42.0 inches of rain, about 795 gallons for every inch that falls.

In Concord, NH 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 Concord Muni Ap station (4.0 mi away). Concord, NH ranks 9th wettest of the 11 cities covered in New Hampshire.

Month by month in Concord

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	2.80	2,225
Feb	2.75	2,186
Mar	3.28	2,607
Apr	3.43	2,726	115
May	3.47	2,758	110
Jun	3.77	2,996	72
Jul	3.62	2,877	91
Aug	3.63	2,885	90
Sep	3.63	2,885	90
Oct	4.43	3,521
Nov	3.44	2,734
Dec	3.70	2,941

Oct is the wettest month (4.43 in, 3,521 gal off the roof); Feb the driest (2.75 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 Concord

Best fit: one 55-gallon barrel, which delivers about 446 gallons to the garden in a normal year (78.6% 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 Concord's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	446	31,726
110 gal	446	31,726
165 gal	446	31,726
275 gal	446	31,726
550 gal	446	31,726
1,000 gal	446	31,726
1,500 gal	446	31,726
2,500 gal	446	31,726
5,000 gal	446	31,726

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 New Hampshire?

No rainwater harvesting regulations

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