Star, ID rainwater: 9,800 gallons off a roof
Star, ID: gallons off the roof each year
9,800gallons a year
That is a 1,500 sq ft asphalt roof under Star, ID's normal 12.3 inches of rain, about 795 gallons for every inch that falls.
Star, 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 Middleton 0.7 Ene station (6.1 mi away). Star, ID ranks 16th wettest of the 26 cities covered in Idaho.
Month by month in Star
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.41 | 1,121 | |
| Feb | 1.03 | 819 | |
| Mar | 1.22 | 970 | |
| Apr | 1.23 | 978 | 389 |
| May | 1.63 | 1,296 | 339 |
| Jun | 0.88 | 699 | 433 |
| Jul | 0.28 | 223 | 507 |
| Aug | 0.21 | 167 | 516 |
| Sep | 0.52 | 413 | 478 |
| Oct | 0.84 | 668 | 438 |
| Nov | 1.17 | 930 | |
| Dec | 1.91 | 1,518 |
Dec is the wettest month (1.91 in, 1,518 gal off the roof); Aug the driest (0.21 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 Star
Best fit: a 1,000-gallon cistern, which delivers about 2,884 gallons to the garden in a normal year (93.0% of its need).
Before you buy, 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 | 8,311 |
| 110 gal | 1,550 | 7,680 |
| 165 gal | 1,870 | 7,360 |
| 275 gal | 2,169 | 7,060 |
| 550 gal | 2,463 | 6,767 |
| 1,000 gal | 2,884 | 6,346 |
| 1,500 gal | 2,884 | 6,346 |
| 2,500 gal | 2,884 | 6,346 |
| 5,000 gal | 2,884 | 6,346 |
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