The Dalles, OR rainwater: 10,849 gallons off a roof
The Dalles, OR: gallons off the roof each year
10,849gallons a year
That is a 1,500 sq ft asphalt roof under The Dalles, OR's normal 13.7 inches of rain, about 795 gallons for every inch that falls.
The Dalles, OR'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 The Dalles Muni Ap station (1.6 mi away). The Dalles, OR ranks 50th wettest of the 57 cities covered in Oregon.
Month by month in The Dalles
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.38 | 1,892 | |
| Feb | 1.58 | 1,256 | |
| Mar | 1.18 | 938 | |
| Apr | 0.83 | 660 | 439 |
| May | 0.76 | 604 | 448 |
| Jun | 0.48 | 382 | 482 |
| Jul | 0.16 | 127 | 522 |
| Aug | 0.16 | 127 | 522 |
| Sep | 0.33 | 262 | 501 |
| Oct | 1.14 | 906 | 400 |
| Nov | 1.97 | 1,566 | |
| Dec | 2.68 | 2,130 |
Dec is the wettest month (2.68 in, 2,130 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.
Which tank size is worth it in The Dalles
Best fit: a 1,000-gallon cistern, which delivers about 2,833 gallons to the garden in a normal year (85.5% 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 | 770 | 9,434 |
| 110 gal | 1,458 | 8,746 |
| 165 gal | 1,842 | 8,362 |
| 275 gal | 2,108 | 8,096 |
| 550 gal | 2,383 | 7,821 |
| 1,000 gal | 2,833 | 7,371 |
| 1,500 gal | 3,121 | 7,083 |
| 2,500 gal | 3,121 | 7,083 |
| 5,000 gal | 3,121 | 7,083 |
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 Oregon?
Collecting and using rain from an artificial impervious surface (e.g. a rooftop) is an exempt use: no water right application, permit or certificate needed. Statute sets no storage cap in this section.
Checked against the current source on 2026-11-06. Source