Alamo, TX rainwater: 21,754 gallons off a roof
Alamo, TX: gallons off the roof each year
21,754gallons a year
That is a 1,500 sq ft asphalt roof under Alamo, TX's normal 27.4 inches of rain, about 795 gallons for every inch that falls.
Alamo, TX has gaps between storms long enough to drain a single barrel. Around 165 gallons of storage catches most of what is worth catching.
Rainfall: NOAA 1991-2020 climate normals, the Mcallen 2.4 Ne station (7.5 mi away). Alamo, TX ranks 211th wettest of the 252 cities covered in Texas.
Month by month in Alamo
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 0.98 | 779 | |
| Feb | 1.02 | 811 | |
| Mar | 1.96 | 1,558 | |
| Apr | 1.47 | 1,168 | 359 |
| May | 1.93 | 1,534 | 302 |
| Jun | 2.61 | 2,074 | 217 |
| Jul | 4.53 | 3,600 | |
| Aug | 2.31 | 1,836 | 254 |
| Sep | 4.83 | 3,839 | |
| Oct | 2.69 | 2,138 | 207 |
| Nov | 1.59 | 1,264 | |
| Dec | 1.45 | 1,152 |
Sep is the wettest month (4.83 in, 3,839 gal off the roof); Jan the driest (0.98 in). Garden shortfall is what a 200 sq ft vegetable bed needs beyond the rain that lands on it, April to October.
Which tank size is worth it in Alamo
Best fit: 3 linked 55-gallon barrels, which delivers about 1,227 gallons to the garden in a normal year (91.6% of its need).
If you buy one, link barrels with a short hose at the base so they fill and drain together, and check the overflow points away from the house.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 783 | 20,536 |
| 110 gal | 1,094 | 20,225 |
| 165 gal | 1,227 | 20,092 |
| 275 gal | 1,229 | 20,090 |
| 550 gal | 1,229 | 20,090 |
| 1,000 gal | 1,229 | 20,090 |
| 1,500 gal | 1,229 | 20,090 |
| 2,500 gal | 1,229 | 20,090 |
| 5,000 gal | 1,229 | 20,090 |
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