Pasco, WA rainwater: 6,056 gallons off a roof
Rainwater from a roof in Pasco, WA
6,056gallons a year
That is a 1,500 sq ft asphalt roof under Pasco, WA's normal 7.6 inches of rain, about 795 gallons for every inch that falls.
Pasco, WA'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 Pasco Tri Cities Ap station (0.2 mi away). Pasco, WA ranks 91st wettest of the 91 cities covered in Washington.
Month by month in Pasco
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 1.03 | 819 | |
| Feb | 0.63 | 501 | |
| Mar | 0.69 | 548 | |
| Apr | 0.66 | 525 | 460 |
| May | 0.71 | 564 | 454 |
| Jun | 0.61 | 485 | 466 |
| Jul | 0.15 | 119 | 524 |
| Aug | 0.27 | 215 | 509 |
| Sep | 0.31 | 246 | 504 |
| Oct | 0.66 | 525 | 460 |
| Nov | 0.87 | 691 | |
| Dec | 1.03 | 819 |
Jan is the wettest month (1.03 in, 819 gal off the roof); Jul the driest (0.15 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 Pasco?
Best fit: a 1,000-gallon cistern, which delivers about 2,938 gallons to the garden in a normal year (87.0% 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 | 605 | 4,957 |
| 110 gal | 1,201 | 4,361 |
| 165 gal | 1,696 | 3,866 |
| 275 gal | 2,213 | 3,349 |
| 550 gal | 2,488 | 3,074 |
| 1,000 gal | 2,938 | 2,624 |
| 1,500 gal | 3,222 | 2,340 |
| 2,500 gal | 3,222 | 2,180 |
| 5,000 gal | 3,222 | 0 |
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 Washington?
Collecting and storing rooftop rainwater for use on site needs no water right permit, provided the roof is part of a fixed above-ground structure whose primary purpose is not rain collection. Ecology may set local restrictions on new systems if they harm instream values or existing water rights. No state storage cap in the policy.
Checked against the current source on 2026-11-06. Source