Oak Park, MI rainwater: 27,731 gallons off a roof

Oak Park, MI: gallons off the roof each year

27,731gallons a year

That is a 1,500 sq ft asphalt roof under Oak Park, MI's normal 34.9 inches of rain, about 795 gallons for every inch that falls.

In Oak Park, MI 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 Dearborn #2 station (8.2 mi away). Oak Park, MI ranks 41st wettest of the 90 cities covered in Michigan.

Month by month in Oak Park

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	2.07	1,645
Feb	2.06	1,637
Mar	2.50	1,987
Apr	3.23	2,567	140
May	3.69	2,933	82
Jun	3.67	2,917	85
Jul	3.39	2,694	120
Aug	3.51	2,790	105
Sep	3.04	2,416	163
Oct	2.76	2,194	198
Nov	2.62	2,082
Dec	2.35	1,868

May is the wettest month (3.69 in, 2,933 gal off the roof); Feb the driest (2.06 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 Oak Park

Best fit: one 55-gallon barrel, which delivers about 692 gallons to the garden in a normal year (77.5% 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 Oak Park's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	692	25,869
110 gal	692	25,869
165 gal	692	25,869
275 gal	692	25,869
550 gal	692	25,869
1,000 gal	692	25,869
1,500 gal	692	25,869
2,500 gal	692	25,869
5,000 gal	692	25,869

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 Michigan?

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