Littleton, CO rainwater: 14,847 gallons off a roof
Littleton, CO: gallons off the roof each year
14,847gallons a year
That is a 1,500 sq ft asphalt roof under Littleton, CO's normal 18.7 inches of rain, about 795 gallons for every inch that falls.
In Littleton, 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 Denver 9.4 S station (2.5 mi away). Littleton, CO ranks 11th wettest of the 53 cities covered in Colorado.
Month by month in Littleton
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.61 | 485 | |
| Feb | 0.78 | 620 | |
| Mar | 1.64 | 1,303 | |
| Apr | 2.48 | 1,971 | 233 |
| May | 2.56 | 2,035 | 223 |
| Jun | 1.77 | 1,407 | 322 |
| Jul | 2.33 | 1,852 | 252 |
| Aug | 2.04 | 1,621 | 288 |
| Sep | 1.51 | 1,200 | 354 |
| Oct | 1.52 | 1,208 | 353 |
| Nov | 0.88 | 699 | |
| Dec | 0.56 | 445 |
May is the wettest month (2.56 in, 2,035 gal off the roof); Dec the driest (0.56 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 Littleton
Best fit: 2 linked 55-gallon barrels, which delivers about 1,748 gallons to the garden in a normal year (86.3% 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 Littleton's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,432 | 12,784 |
| 110 gal | 1,748 | 12,469 |
| 165 gal (over cap) | 1,748 | 12,469 |
| 275 gal (over cap) | 1,748 | 12,469 |
| 550 gal (over cap) | 1,748 | 12,469 |
| 1,000 gal (over cap) | 1,748 | 12,469 |
| 1,500 gal (over cap) | 1,748 | 12,469 |
| 2,500 gal (over cap) | 1,748 | 12,469 |
| 5,000 gal (over cap) | 1,748 | 12,469 |
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