Key Biscayne, FL rainwater: 43,977 gallons off a roof
How much rain a roof in Key Biscayne, FL collects
43,977gallons a year
That is a 1,500 sq ft asphalt roof under Key Biscayne, FL's normal 55.3 inches of rain, about 795 gallons for every inch that falls.
In Key Biscayne, FL 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 Cape Florida station (1.4 mi away). Key Biscayne, FL ranks 95th wettest of the 173 cities covered in Florida.
Month by month in Key Biscayne
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.44 | 1,939 | |
| Feb | 2.00 | 1,590 | |
| Mar | 2.37 | 1,884 | |
| Apr | 3.17 | 2,520 | 147 |
| May | 5.67 | 4,507 | |
| Jun | 7.37 | 5,858 | |
| Jul | 5.64 | 4,483 | |
| Aug | 7.05 | 5,603 | |
| Sep | 7.54 | 5,993 | |
| Oct | 6.33 | 5,031 | |
| Nov | 3.51 | 2,790 | |
| Dec | 2.24 | 1,780 |
Sep is the wettest month (7.54 in, 5,993 gal off the roof); Feb the driest (2.00 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 Key Biscayne
Best fit: one 55-gallon barrel, which delivers about 128 gallons to the garden in a normal year (87.0% 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 Key Biscayne's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 128 | 42,739 |
| 110 gal | 128 | 42,739 |
| 165 gal | 128 | 42,739 |
| 275 gal | 128 | 42,739 |
| 550 gal | 128 | 42,739 |
| 1,000 gal | 128 | 42,739 |
| 1,500 gal | 128 | 42,739 |
| 2,500 gal | 128 | 42,739 |
| 5,000 gal | 128 | 42,739 |
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 Florida?
Legal. Florida approves onsite non-potable use of rainwater for landscape irrigation, vehicle washing, filling pools and fountains and, in some local jurisdictions, toilet/urinal flushing (Florida Plumbing Code). No state storage cap or registration for non-potable collection.
Checked against the current source on 2026-11-06. Source