London, OH rainwater: 33,604 gallons off a roof
London, OH: gallons off the roof each year
33,604gallons a year
That is a 1,500 sq ft asphalt roof under London, OH's normal 42.3 inches of rain, about 795 gallons for every inch that falls.
In London, OH 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 London Fish Hatchery station (3.8 mi away). London, OH ranks 76th wettest of the 176 cities covered in Ohio.
Month by month in London
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 3.12 | 2,480 | |
| Feb | 2.28 | 1,812 | |
| Mar | 3.70 | 2,941 | |
| Apr | 4.05 | 3,219 | 37 |
| May | 4.67 | 3,712 | |
| Jun | 4.71 | 3,744 | |
| Jul | 4.96 | 3,942 | |
| Aug | 2.87 | 2,281 | 185 |
| Sep | 2.91 | 2,313 | 180 |
| Oct | 2.83 | 2,249 | 190 |
| Nov | 2.96 | 2,353 | |
| Dec | 3.22 | 2,559 |
Jul is the wettest month (4.96 in, 3,942 gal off the roof); Feb the driest (2.28 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 London
Best fit: one 55-gallon barrel, which delivers about 497 gallons to the garden in a normal year (84.1% of its need).
If you buy one, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of London's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 497 | 31,953 |
| 110 gal | 497 | 31,953 |
| 165 gal | 497 | 31,953 |
| 275 gal | 497 | 31,953 |
| 550 gal | 497 | 31,953 |
| 1,000 gal | 497 | 31,953 |
| 1,500 gal | 497 | 31,953 |
| 2,500 gal | 497 | 31,953 |
| 5,000 gal | 497 | 31,953 |
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 Ohio?
Legal. Ohio regulates rainwater cisterns used as a drinking-water source as private water systems (OAC chapter 3701-28): local health department permit, continuous disinfection and filtration. No state rule restricting non-potable collection or storage size.
Checked against the current source on 2026-11-06. Source