Grand Junction, CO rainwater: 9,299 gallons off a roof
Grand Junction, CO: gallons off the roof each year
9,299gallons a year
That is a 1,500 sq ft asphalt roof under Grand Junction, CO's normal 11.7 inches of rain, about 795 gallons for every inch that falls.
Grand Junction, CO has gaps between storms long enough to drain a single barrel. Around 110 gallons of storage catches most of what is worth catching.
Rainfall: NOAA 1991-2020 climate normals, the Grand Junction 3.6 W station (2.8 mi away). Grand Junction, CO ranks 51st wettest of the 53 cities covered in Colorado.
Month by month in Grand Junction
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.76 | 604 | |
| Feb | 0.65 | 517 | |
| Mar | 1.07 | 850 | |
| Apr | 1.09 | 866 | 406 |
| May | 1.13 | 898 | 401 |
| Jun | 0.58 | 461 | 470 |
| Jul | 0.75 | 596 | 449 |
| Aug | 1.26 | 1,001 | 385 |
| Sep | 1.35 | 1,073 | 374 |
| Oct | 1.52 | 1,208 | 353 |
| Nov | 0.81 | 644 | |
| Dec | 0.73 | 580 |
Oct is the wettest month (1.52 in, 1,208 gal off the roof); Jun the driest (0.58 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 Grand Junction
Best fit: 2 linked 55-gallon barrels, which delivers about 2,093 gallons to the garden in a normal year (73.7% of its need).
Colorado caps storage at 110 gallons, below the 165 gallons that would pay off here. The table marks sizes over the cap.
Before you buy, link barrels with a short hose at the base so they fill and drain together, and check the overflow points away from the house.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,155 | 7,679 |
| 110 gal | 2,093 | 6,742 |
| 165 gal (over cap) | 2,416 | 6,418 |
| 275 gal (over cap) | 2,578 | 6,256 |
| 550 gal (over cap) | 2,578 | 6,256 |
| 1,000 gal (over cap) | 2,578 | 6,256 |
| 1,500 gal (over cap) | 2,578 | 6,256 |
| 2,500 gal (over cap) | 2,578 | 6,256 |
| 5,000 gal (over cap) | 2,578 | 6,256 |
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 Colorado?
Most households may use rain barrels: a maximum of two rain barrels with a combined storage of 110 gallons or less per household, rooftop runoff only, used outdoors on the same property (HB16-1005). Larger rooftop collection only for qualifying well-permit holders (SB09-080) or pilot projects (HB09-1129).
Checked against the current source on 2026-11-06. Source