Ankeny, IA rainwater: 29,448 gallons off a roof

Rainwater from a roof in Ankeny, IA

29,448gallons a year

That is a 1,500 sq ft asphalt roof under Ankeny, IA's normal 37.1 inches of rain, about 795 gallons for every inch that falls.

In Ankeny, 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 Ankeny station (2.5 mi away). Ankeny, IA ranks 23rd wettest of the 41 cities covered in Iowa.

Month by month in Ankeny

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	0.97	771
Feb	0.99	787
Mar	2.01	1,598
Apr	4.00	3,179	44
May	5.26	4,181
Jun	5.37	4,268
Jul	4.19	3,330	20
Aug	4.72	3,751
Sep	3.62	2,877	91
Oct	2.67	2,122	209
Nov	1.86	1,478
Dec	1.39	1,105

Jun is the wettest month (5.37 in, 4,268 gal off the roof); Jan the driest (0.97 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 Ankeny?

Best fit: one 55-gallon barrel, which delivers about 301 gallons to the garden in a normal year (82.7% 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 Ankeny's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	301	28,171
110 gal	301	28,171
165 gal	301	28,171
275 gal	301	28,171
550 gal	301	28,171
1,000 gal	301	28,171
1,500 gal	301	28,171
2,500 gal	301	28,171
5,000 gal	301	28,171

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