Oklahoma City, OK rainwater: 29,368 gallons off a roof
Oklahoma City, OK: gallons off the roof each year
29,368gallons a year
That is a 1,500 sq ft asphalt roof under Oklahoma City, OK's normal 37.0 inches of rain, about 795 gallons for every inch that falls.
In Oklahoma City, 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 Oklahoma City station (6.3 mi away). Oklahoma City, OK ranks 25th wettest of the 45 cities covered in Oklahoma.
Month by month in Oklahoma City
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.28 | 1,017 | |
| Feb | 1.58 | 1,256 | |
| Mar | 2.66 | 2,114 | |
| Apr | 3.61 | 2,869 | 92 |
| May | 5.48 | 4,356 | |
| Jun | 4.83 | 3,839 | |
| Jul | 3.32 | 2,639 | 128 |
| Aug | 3.37 | 2,678 | 122 |
| Sep | 3.91 | 3,108 | 55 |
| Oct | 3.25 | 2,583 | 137 |
| Nov | 1.80 | 1,431 | |
| Dec | 1.86 | 1,478 |
May is the wettest month (5.48 in, 4,356 gal off the roof); Jan the driest (1.28 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 Oklahoma City
Best fit: one 55-gallon barrel, which delivers about 453 gallons to the garden in a normal year (84.7% 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 Oklahoma City's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 453 | 28,135 |
| 110 gal | 453 | 28,135 |
| 165 gal | 453 | 28,135 |
| 275 gal | 453 | 28,135 |
| 550 gal | 453 | 28,135 |
| 1,000 gal | 453 | 28,135 |
| 1,500 gal | 453 | 28,135 |
| 2,500 gal | 453 | 28,135 |
| 5,000 gal | 453 | 28,135 |
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