Parker, CO rainwater: 14,903 gallons off a roof
Rainwater from a roof in Parker, CO
14,903gallons a year
That is a 1,500 sq ft asphalt roof under Parker, CO's normal 18.8 inches of rain, about 795 gallons for every inch that falls.
In Parker, 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 Parker 2.0 Wsw station (1.3 mi away). Parker, CO ranks 10th wettest of the 53 cities covered in Colorado.
Month by month in Parker
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.62 | 493 | |
| Feb | 0.71 | 564 | |
| Mar | 1.44 | 1,145 | |
| Apr | 2.24 | 1,780 | 263 |
| May | 2.56 | 2,035 | 223 |
| Jun | 2.08 | 1,653 | 283 |
| Jul | 2.39 | 1,900 | 244 |
| Aug | 2.35 | 1,868 | 249 |
| Sep | 1.41 | 1,121 | 367 |
| Oct | 1.37 | 1,089 | 372 |
| Nov | 0.92 | 731 | |
| Dec | 0.66 | 525 |
May is the wettest month (2.56 in, 2,035 gal off the roof); Jan the driest (0.62 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 Parker?
Best fit: 2 linked 55-gallon barrels, which delivers about 1,739 gallons to the garden in a normal year (86.9% of its need).
If you buy one, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Parker's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,407 | 12,896 |
| 110 gal | 1,739 | 12,563 |
| 165 gal (over cap) | 1,739 | 12,563 |
| 275 gal (over cap) | 1,739 | 12,563 |
| 550 gal (over cap) | 1,739 | 12,563 |
| 1,000 gal (over cap) | 1,739 | 12,563 |
| 1,500 gal (over cap) | 1,739 | 12,563 |
| 2,500 gal (over cap) | 1,739 | 12,563 |
| 5,000 gal (over cap) | 1,739 | 12,563 |
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