Novi, MI rainwater: 27,572 gallons off a roof

How much rain a roof in Novi, MI collects

27,572gallons a year

That is a 1,500 sq ft asphalt roof under Novi, MI's normal 34.7 inches of rain, about 795 gallons for every inch that falls.

In Novi, 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 Farmington Hills 1.4 N station (5.8 mi away). Novi, MI ranks 45th wettest of the 90 cities covered in Michigan.

Month by month in Novi

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	2.29	1,820
Feb	1.95	1,550
Mar	2.50	1,987
Apr	3.25	2,583	137
May	3.74	2,973	76
Jun	3.09	2,456	157
Jul	3.60	2,861	94
Aug	3.39	2,694	120
Sep	3.29	2,615	132
Oct	2.81	2,233	192
Nov	2.66	2,114
Dec	2.12	1,685

May is the wettest month (3.74 in, 2,973 gal off the roof); Feb the driest (1.95 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 Novi

Best fit: one 55-gallon barrel, which delivers about 703 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 Novi's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	703	25,699
110 gal	703	25,699
165 gal	703	25,699
275 gal	703	25,699
550 gal	703	25,699
1,000 gal	703	25,699
1,500 gal	703	25,699
2,500 gal	703	25,699
5,000 gal	703	25,699

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