Allen, TX rainwater: 32,396 gallons off a roof
Rainwater from a roof in Allen, TX
32,396gallons a year
That is a 1,500 sq ft asphalt roof under Allen, TX's normal 40.8 inches of rain, about 795 gallons for every inch that falls.
In Allen, TX 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 Fairview 1.5 Ese station (4.7 mi away). Allen, TX ranks 99th wettest of the 252 cities covered in Texas.
Month by month in Allen
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.87 | 2,281 | |
| Feb | 2.80 | 2,225 | |
| Mar | 3.65 | 2,901 | |
| Apr | 3.63 | 2,885 | 90 |
| May | 4.93 | 3,918 | |
| Jun | 3.74 | 2,973 | 76 |
| Jul | 2.20 | 1,749 | 268 |
| Aug | 2.31 | 1,836 | 254 |
| Sep | 3.20 | 2,543 | 143 |
| Oct | 4.79 | 3,807 | |
| Nov | 3.20 | 2,543 | |
| Dec | 3.44 | 2,734 |
May is the wettest month (4.93 in, 3,918 gal off the roof); Jul the driest (2.20 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 Allen
Best fit: 2 linked 55-gallon barrels, which delivers about 734 gallons to the garden in a normal year (88.3% 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 Allen's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 621 | 30,995 |
| 110 gal | 734 | 30,882 |
| 165 gal | 734 | 30,882 |
| 275 gal | 734 | 30,882 |
| 550 gal | 734 | 30,882 |
| 1,000 gal | 734 | 30,882 |
| 1,500 gal | 734 | 30,882 |
| 2,500 gal | 734 | 30,882 |
| 5,000 gal | 734 | 30,882 |
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 Texas?
Rainwater harvesting is legal and encouraged; no state storage cap. HOAs may not adopt new covenants banning rainwater harvesting installations but may require screening. Local taxing units may exempt property with water conservation initiatives from property tax (Tax Code 11.32).
Checked against the current source on 2026-11-06. Source