Thornton, CO rainwater: 13,289 gallons off a roof
Thornton, CO: gallons off the roof each year
13,289gallons a year
That is a 1,500 sq ft asphalt roof under Thornton, CO's normal 16.7 inches of rain, about 795 gallons for every inch that falls.
In Thornton, 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 Thornton 2.1 N station (0.8 mi away). Thornton, CO ranks 26th wettest of the 53 cities covered in Colorado.
Month by month in Thornton
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.54 | 429 | |
| Feb | 0.72 | 572 | |
| Mar | 1.47 | 1,168 | |
| Apr | 2.02 | 1,606 | 290 |
| May | 2.52 | 2,003 | 228 |
| Jun | 1.76 | 1,399 | 323 |
| Jul | 1.90 | 1,510 | 305 |
| Aug | 1.67 | 1,327 | 334 |
| Sep | 1.30 | 1,033 | 380 |
| Oct | 1.27 | 1,009 | 384 |
| Nov | 0.84 | 668 | |
| Dec | 0.71 | 564 |
May is the wettest month (2.52 in, 2,003 gal off the roof); Jan the driest (0.54 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 Thornton
Best fit: 2 linked 55-gallon barrels, which delivers about 1,942 gallons to the garden in a normal year (86.5% of its need).
Before you buy, a 55-gallon barrel with a downspout diverter is the whole job. Check that the overflow points away from your foundation, because most of Thornton's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 1,393 | 11,311 |
| 110 gal | 1,942 | 10,762 |
| 165 gal (over cap) | 1,963 | 10,741 |
| 275 gal (over cap) | 1,963 | 10,741 |
| 550 gal (over cap) | 1,963 | 10,741 |
| 1,000 gal (over cap) | 1,963 | 10,741 |
| 1,500 gal (over cap) | 1,963 | 10,741 |
| 2,500 gal (over cap) | 1,963 | 10,741 |
| 5,000 gal (over cap) | 1,963 | 10,741 |
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