Frederick, CO rainwater: 11,922 gallons off a roof
Rainwater from a roof in Frederick, CO
11,922gallons a year
That is a 1,500 sq ft asphalt roof under Frederick, CO's normal 15.0 inches of rain, about 795 gallons for every inch that falls.
In Frederick, 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 Frederick 2.0 Nw station (1.1 mi away). Frederick, CO ranks 36th wettest of the 53 cities covered in Colorado.
Month by month in Frederick
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.48 | 382 | |
| Feb | 0.48 | 382 | |
| Mar | 1.21 | 962 | |
| Apr | 1.88 | 1,494 | 308 |
| May | 2.50 | 1,987 | 231 |
| Jun | 1.61 | 1,280 | 342 |
| Jul | 1.49 | 1,184 | 357 |
| Aug | 1.61 | 1,280 | 342 |
| Sep | 1.53 | 1,216 | 352 |
| Oct | 1.04 | 827 | 413 |
| Nov | 0.66 | 525 | |
| Dec | 0.51 | 405 |
May is the wettest month (2.50 in, 1,987 gal off the roof); Jan the driest (0.48 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
What size rain barrel for Frederick
Best fit: 2 linked 55-gallon barrels, which delivers about 2,038 gallons to the garden in a normal year (87.0% 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 Frederick's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,388 | 9,994 |
| 110 gal | 2,038 | 9,344 |
| 165 gal (over cap) | 2,065 | 9,317 |
| 275 gal (over cap) | 2,065 | 9,317 |
| 550 gal (over cap) | 2,065 | 9,317 |
| 1,000 gal (over cap) | 2,065 | 9,317 |
| 1,500 gal (over cap) | 2,065 | 9,317 |
| 2,500 gal (over cap) | 2,065 | 9,317 |
| 5,000 gal (over cap) | 2,065 | 9,317 |
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