Kuna, ID rainwater: 10,150 gallons off a roof
How much rain a roof in Kuna, ID collects
10,150gallons a year
That is a 1,500 sq ft asphalt roof under Kuna, ID's normal 12.8 inches of rain, about 795 gallons for every inch that falls.
Kuna, ID's rain arrives in a wet season and stops, so storage is what matters. It takes a cistern of 1,000 gallons to carry spring rain into the dry months.
Rainfall: NOAA 1991-2020 climate normals, the Meridian 4.8 Sse station (3.1 mi away). Kuna, ID ranks 13th wettest of the 26 cities covered in Idaho.
Month by month in Kuna
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.43 | 1,137 | |
| Feb | 0.99 | 787 | |
| Mar | 1.66 | 1,319 | |
| Apr | 1.55 | 1,232 | 349 |
| May | 1.66 | 1,319 | 335 |
| Jun | 0.83 | 660 | 439 |
| Jul | 0.37 | 294 | 496 |
| Aug | 0.32 | 254 | 502 |
| Sep | 0.56 | 445 | 473 |
| Oct | 0.82 | 652 | 440 |
| Nov | 1.09 | 866 | |
| Dec | 1.49 | 1,184 |
Mar is the wettest month (1.66 in, 1,319 gal off the roof); Aug the driest (0.32 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 Kuna?
Best fit: a 1,000-gallon cistern, which delivers about 2,813 gallons to the garden in a normal year (92.7% of its need).
If you buy one, ask about a rebate first: cistern-sized storage costs real money, and a buried or tall tank may need a permit. Place it where a full tank (about 8.3 lb a gallon) sits on firm, level ground.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 805 | 8,535 |
| 110 gal | 1,322 | 8,019 |
| 165 gal | 1,621 | 7,719 |
| 275 gal | 2,039 | 7,301 |
| 550 gal | 2,363 | 6,977 |
| 1,000 gal | 2,813 | 6,527 |
| 1,500 gal | 2,855 | 6,485 |
| 2,500 gal | 2,855 | 6,485 |
| 5,000 gal | 2,855 | 6,485 |
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 Idaho?
Allowed through a legal clarification made by the Office of the Attorney General
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