Norman, OK rainwater: 29,893 gallons off a roof
Norman, OK: gallons off the roof each year
29,893gallons a year
That is a 1,500 sq ft asphalt roof under Norman, OK's normal 37.6 inches of rain, about 795 gallons for every inch that falls.
In Norman, 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 Hall Park 2.0 Sse station (3.0 mi away). Norman, OK ranks 21st wettest of the 45 cities covered in Oklahoma.
Month by month in Norman
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.39 | 1,105 | |
| Feb | 1.57 | 1,248 | |
| Mar | 2.74 | 2,178 | |
| Apr | 3.55 | 2,822 | 100 |
| May | 5.41 | 4,300 | |
| Jun | 4.64 | 3,688 | |
| Jul | 3.54 | 2,814 | 101 |
| Aug | 3.59 | 2,853 | 95 |
| Sep | 3.92 | 3,116 | 54 |
| Oct | 3.27 | 2,599 | 135 |
| Nov | 1.97 | 1,566 | |
| Dec | 2.02 | 1,606 |
May is the wettest month (5.41 in, 4,300 gal off the roof); Jan the driest (1.39 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 Norman
Best fit: one 55-gallon barrel, which delivers about 402 gallons to the garden in a normal year (83.1% 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 Norman's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 402 | 28,651 |
| 110 gal | 402 | 28,651 |
| 165 gal | 402 | 28,651 |
| 275 gal | 402 | 28,651 |
| 550 gal | 402 | 28,651 |
| 1,000 gal | 402 | 28,651 |
| 1,500 gal | 402 | 28,651 |
| 2,500 gal | 402 | 28,651 |
| 5,000 gal | 402 | 28,651 |
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