Hilton Head Island, SC rainwater: 36,831 gallons off a roof
Hilton Head Island, SC: gallons off the roof each year
36,831gallons a year
That is a 1,500 sq ft asphalt roof under Hilton Head Island, SC's normal 46.3 inches of rain, about 795 gallons for every inch that falls.
In Hilton Head Island, SC 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 Hilton Head Island 2.7 E station (2.2 mi away). Hilton Head Island, SC ranks 33rd wettest of the 42 cities covered in South Carolina.
Month by month in Hilton Head Island
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 3.58 | 2,845 | |
| Feb | 2.86 | 2,273 | |
| Mar | 3.59 | 2,853 | |
| Apr | 2.38 | 1,892 | 246 |
| May | 2.82 | 2,241 | 191 |
| Jun | 5.28 | 4,197 | |
| Jul | 4.33 | 3,442 | 2 |
| Aug | 6.53 | 5,190 | |
| Sep | 4.97 | 3,950 | |
| Oct | 4.41 | 3,505 | |
| Nov | 2.49 | 1,979 | |
| Dec | 3.10 | 2,464 |
Aug is the wettest month (6.53 in, 5,190 gal off the roof); Apr the driest (2.38 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 Hilton Head Island
Best fit: one 55-gallon barrel, which delivers about 370 gallons to the garden in a normal year (84.3% 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 Hilton Head Island's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 370 | 35,441 |
| 110 gal | 375 | 35,437 |
| 165 gal | 375 | 35,437 |
| 275 gal | 375 | 35,437 |
| 550 gal | 375 | 35,437 |
| 1,000 gal | 375 | 35,437 |
| 1,500 gal | 375 | 35,437 |
| 2,500 gal | 375 | 35,437 |
| 5,000 gal | 375 | 35,437 |
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 South Carolina?
No rainwater harvesting regulations
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