Westminster, CO rainwater: 13,758 gallons off a roof
Rainwater from a roof in Westminster, CO
13,758gallons a year
That is a 1,500 sq ft asphalt roof under Westminster, CO's normal 17.3 inches of rain, about 795 gallons for every inch that falls.
In Westminster, CO a single barrel does most of the work. Storms come often enough that a small tank refills before it runs dry, and a bigger one would mostly sit full.
Rainfall: NOAA 1991-2020 climate normals, the Westminster 0.8 Ese station (1.3 mi away). Westminster, CO ranks 23rd wettest of the 53 cities covered in Colorado.
Month by month in Westminster
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.72 | 572 | |
| Feb | 0.82 | 652 | |
| Mar | 1.60 | 1,272 | |
| Apr | 1.79 | 1,423 | 319 |
| May | 2.78 | 2,210 | 196 |
| Jun | 1.55 | 1,232 | 349 |
| Jul | 1.87 | 1,486 | 309 |
| Aug | 1.75 | 1,391 | 324 |
| Sep | 1.34 | 1,065 | 375 |
| Oct | 1.44 | 1,145 | 363 |
| Nov | 0.89 | 707 | |
| Dec | 0.76 | 604 |
May is the wettest month (2.78 in, 2,210 gal off the roof); Jan the driest (0.72 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 Westminster?
Best fit: 2 linked 55-gallon barrels, which delivers about 1,938 gallons to the garden in a normal year (86.7% of its need).
If you set one up, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Westminster's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,375 | 11,753 |
| 110 gal | 1,938 | 11,191 |
| 165 gal (over cap) | 1,948 | 11,181 |
| 275 gal (over cap) | 1,948 | 11,181 |
| 550 gal (over cap) | 1,948 | 11,181 |
| 1,000 gal (over cap) | 1,948 | 11,181 |
| 1,500 gal (over cap) | 1,948 | 11,181 |
| 2,500 gal (over cap) | 1,948 | 11,181 |
| 5,000 gal (over cap) | 1,948 | 11,181 |
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