Garden City, ID rainwater: 11,390 gallons off a roof
How much rain a roof in Garden City, ID collects
11,390gallons a year
That is a 1,500 sq ft asphalt roof under Garden City, ID's normal 14.3 inches of rain, about 795 gallons for every inch that falls.
Garden City, 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 Boise 5.3 Nw station (1.5 mi away). Garden City, ID ranks 8th wettest of the 26 cities covered in Idaho.
Month by month in Garden City
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.84 | 1,462 | |
| Feb | 1.24 | 986 | |
| Mar | 1.67 | 1,327 | |
| Apr | 1.44 | 1,145 | 363 |
| May | 1.66 | 1,319 | 335 |
| Jun | 1.04 | 827 | 413 |
| Jul | 0.28 | 223 | 507 |
| Aug | 0.27 | 215 | 509 |
| Sep | 0.43 | 342 | 489 |
| Oct | 0.94 | 747 | 425 |
| Nov | 1.40 | 1,113 | |
| Dec | 2.12 | 1,685 |
Dec is the wettest month (2.12 in, 1,685 gal off the roof); Aug the driest (0.27 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 Garden City?
Best fit: a 1,000-gallon cistern, which delivers about 2,779 gallons to the garden in a normal year (91.4% of its need).
If you set one up, 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 | 1,133 | 9,507 |
| 110 gal | 1,711 | 8,929 |
| 165 gal | 2,022 | 8,617 |
| 275 gal | 2,209 | 8,430 |
| 550 gal | 2,484 | 8,155 |
| 1,000 gal | 2,779 | 7,861 |
| 1,500 gal | 2,779 | 7,861 |
| 2,500 gal | 2,779 | 7,861 |
| 5,000 gal | 2,779 | 7,861 |
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