Caldwell, ID rainwater: 9,689 gallons off a roof
Caldwell, ID: gallons off the roof each year
9,689gallons a year
That is a 1,500 sq ft asphalt roof under Caldwell, ID's normal 12.2 inches of rain, about 795 gallons for every inch that falls.
Caldwell, 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 Nampa 4.8 Nnw station (3.3 mi away). Caldwell, ID ranks 18th wettest of the 26 cities covered in Idaho.
Month by month in Caldwell
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.47 | 1,168 | |
| Feb | 0.94 | 747 | |
| Mar | 1.20 | 954 | |
| Apr | 1.19 | 946 | 394 |
| May | 1.50 | 1,192 | 355 |
| Jun | 1.03 | 819 | 414 |
| Jul | 0.29 | 230 | 506 |
| Aug | 0.20 | 159 | 517 |
| Sep | 0.54 | 429 | 475 |
| Oct | 0.81 | 644 | 441 |
| Nov | 1.18 | 938 | |
| Dec | 1.84 | 1,462 |
Dec is the wettest month (1.84 in, 1,462 gal off the roof); Aug the driest (0.20 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 Caldwell
Best fit: a 1,000-gallon cistern, which delivers about 2,886 gallons to the garden in a normal year (93.0% 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 | 919 | 8,199 |
| 110 gal | 1,568 | 7,551 |
| 165 gal | 1,879 | 7,240 |
| 275 gal | 2,178 | 6,941 |
| 550 gal | 2,470 | 6,648 |
| 1,000 gal | 2,886 | 6,233 |
| 1,500 gal | 2,886 | 6,233 |
| 2,500 gal | 2,886 | 6,233 |
| 5,000 gal | 2,886 | 6,233 |
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