Twin Falls, ID rainwater: 7,312 gallons off a roof
How much rain a roof in Twin Falls, ID collects
7,312gallons a year
That is a 1,500 sq ft asphalt roof under Twin Falls, ID's normal 9.2 inches of rain, about 795 gallons for every inch that falls.
Twin Falls, 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 Twin Falls-Kmvt station (1.2 mi away). Twin Falls, ID ranks 26th wettest of the 26 cities covered in Idaho.
Month by month in Twin Falls
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.04 | 827 | |
| Feb | 0.78 | 620 | |
| Mar | 0.87 | 691 | |
| Apr | 1.02 | 811 | 415 |
| May | 1.22 | 970 | 390 |
| Jun | 0.67 | 533 | 459 |
| Jul | 0.16 | 127 | 522 |
| Aug | 0.34 | 270 | 500 |
| Sep | 0.33 | 262 | 501 |
| Oct | 0.70 | 556 | 455 |
| Nov | 0.76 | 604 | |
| Dec | 1.31 | 1,041 |
Dec is the wettest month (1.31 in, 1,041 gal off the roof); Jul the driest (0.16 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 Twin Falls?
Best fit: a 1,000-gallon cistern, which delivers about 2,971 gallons to the garden in a normal year (91.6% 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 | 812 | 6,036 |
| 110 gal | 1,516 | 5,332 |
| 165 gal | 1,854 | 4,993 |
| 275 gal | 2,246 | 4,601 |
| 550 gal | 2,521 | 4,326 |
| 1,000 gal | 2,971 | 3,876 |
| 1,500 gal | 3,040 | 3,807 |
| 2,500 gal | 3,040 | 3,807 |
| 5,000 gal | 3,040 | 2,614 |
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