Lancaster, PA rainwater: 35,091 gallons off a roof

Rainwater from a roof in Lancaster, PA

35,091gallons a year

That is a 1,500 sq ft asphalt roof under Lancaster, PA's normal 44.2 inches of rain, about 795 gallons for every inch that falls.

In Lancaster, PA 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 Lancaster 2ne Fltr Plt station (1.5 mi away). Lancaster, PA ranks 37th wettest of the 68 cities covered in Pennsylvania.

Month by month in Lancaster

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	3.01	2,392
Feb	2.52	2,003
Mar	3.50	2,782
Apr	3.54	2,814	101
May	3.65	2,901	87
Jun	4.09	3,251	32
Jul	4.51	3,585
Aug	3.60	2,861	94
Sep	4.82	3,831
Oct	4.18	3,322	21
Nov	3.26	2,591
Dec	3.47	2,758

Sep is the wettest month (4.82 in, 3,831 gal off the roof); Feb the driest (2.52 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 Lancaster?

Best fit: one 55-gallon barrel, which delivers about 262 gallons to the garden in a normal year (78.1% 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 Lancaster's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	262	33,673
110 gal	262	33,673
165 gal	262	33,673
275 gal	262	33,673
550 gal	262	33,673
1,000 gal	262	33,673
1,500 gal	262	33,673
2,500 gal	262	33,673
5,000 gal	262	33,673

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 Pennsylvania?

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