Spencer, IA rainwater: 24,631 gallons off a roof

Spencer, IA: gallons off the roof each year

24,631gallons a year

That is a 1,500 sq ft asphalt roof under Spencer, IA's normal 31.0 inches of rain, about 795 gallons for every inch that falls.

In Spencer, IA 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 Spencer 1 N station (1.3 mi away). Spencer, IA ranks 40th wettest of the 41 cities covered in Iowa.

Month by month in Spencer

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	0.72	572
Feb	0.79	628
Mar	1.66	1,319
Apr	3.49	2,774	107
May	4.19	3,330	20
Jun	4.60	3,656
Jul	3.74	2,973	76
Aug	3.77	2,996	72
Sep	3.29	2,615	132
Oct	2.35	1,868	249
Nov	1.41	1,121
Dec	0.98	779

Jun is the wettest month (4.60 in, 3,656 gal off the roof); Jan the driest (0.72 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 Spencer

Best fit: one 55-gallon barrel, which delivers about 535 gallons to the garden in a normal year (81.4% of its need).

Before you buy, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Spencer's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	535	23,181
110 gal	535	23,181
165 gal	535	23,181
275 gal	535	23,181
550 gal	535	23,181
1,000 gal	535	23,181
1,500 gal	535	23,181
2,500 gal	535	23,181
5,000 gal	535	23,181

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 Iowa?

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