Altus, OK rainwater: 23,065 gallons off a roof

Rainwater from a roof in Altus, OK

23,065gallons a year

That is a 1,500 sq ft asphalt roof under Altus, OK's normal 29.0 inches of rain, about 795 gallons for every inch that falls.

In Altus, OK 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 Altus 4.8 Nnw station (4.4 mi away). Altus, OK ranks 43rd wettest of the 45 cities covered in Oklahoma.

Month by month in Altus

Month	Rain (in)	Off the roof (gal)	Garden shortfall (gal)
Jan	1.13	898
Feb	1.04	827
Mar	2.02	1,606
Apr	2.94	2,337	176
May	4.05	3,219	37
Jun	3.95	3,139	50
Jul	2.29	1,820	257
Aug	2.95	2,345	175
Sep	2.49	1,979	232
Oct	3.20	2,543	143
Nov	1.72	1,367
Dec	1.24	986

May is the wettest month (4.05 in, 3,219 gal off the roof); Feb the driest (1.04 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.

What size rain barrel for Altus

Best fit: one 55-gallon barrel, which delivers about 916 gallons to the garden in a normal year (85.6% 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 Altus's roof water will pass straight through it.

Tank	Water used (gal/yr)	Spills over (gal/yr)
55 gal	916	21,474
110 gal	925	21,465
165 gal	925	21,465
275 gal	925	21,465
550 gal	925	21,465
1,000 gal	925	21,465
1,500 gal	925	21,465
2,500 gal	925	21,465
5,000 gal	925	21,465

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 Oklahoma?

Encouraged through state legislation: Water for 2060 Act

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