Alpharetta, GA rainwater: 43,698 gallons off a roof
Rainwater from a roof in Alpharetta, GA
43,698gallons a year
That is a 1,500 sq ft asphalt roof under Alpharetta, GA's normal 55.0 inches of rain, about 795 gallons for every inch that falls.
In Alpharetta, GA 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 Johns Creek 3.0 Ssw station (5.5 mi away). Alpharetta, GA ranks 18th wettest of the 101 cities covered in Georgia.
Month by month in Alpharetta
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 4.95 | 3,934 | |
| Feb | 4.81 | 3,823 | |
| Mar | 5.05 | 4,014 | |
| Apr | 3.94 | 3,132 | 51 |
| May | 4.04 | 3,211 | 39 |
| Jun | 4.61 | 3,664 | |
| Jul | 5.65 | 4,491 | |
| Aug | 4.40 | 3,497 | |
| Sep | 4.26 | 3,386 | 11 |
| Oct | 3.90 | 3,100 | 56 |
| Nov | 4.39 | 3,489 | |
| Dec | 4.98 | 3,958 |
Jul is the wettest month (5.65 in, 4,491 gal off the roof); Oct the driest (3.90 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
Barrel or cistern in Alpharetta?
Best fit: one 55-gallon barrel, which delivers about 129 gallons to the garden in a normal year (82.1% 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 Alpharetta's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 129 | 42,340 |
| 110 gal | 129 | 42,340 |
| 165 gal | 129 | 42,340 |
| 275 gal | 129 | 42,340 |
| 550 gal | 129 | 42,340 |
| 1,000 gal | 129 | 42,340 |
| 1,500 gal | 129 | 42,340 |
| 2,500 gal | 129 | 42,340 |
| 5,000 gal | 129 | 42,340 |
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 Georgia?
Legal. Outdoor irrigation use is unrestricted; indoor non-potable systems must follow Appendix I 'Rainwater Recycling Systems' of the Georgia amendments to the state plumbing code. No state storage cap; potable use depends on local rules.
Checked against the current source on 2026-11-06. Source