San Marcos, TX rainwater: 29,050 gallons off a roof
How much rain a roof in San Marcos, TX collects
29,050gallons a year
That is a 1,500 sq ft asphalt roof under San Marcos, TX's normal 36.6 inches of rain, about 795 gallons for every inch that falls.
In San Marcos, 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 San Marcos station (1.0 mi away). San Marcos, TX ranks 159th wettest of the 252 cities covered in Texas.
Month by month in San Marcos
| Month | Rain (in) | Off the roof (gal) | Garden shortfall (gal) |
|---|---|---|---|
| Jan | 2.41 | 1,915 | |
| Feb | 1.73 | 1,375 | |
| Mar | 2.76 | 2,194 | |
| Apr | 3.20 | 2,543 | 143 |
| May | 4.53 | 3,600 | |
| Jun | 3.57 | 2,837 | 97 |
| Jul | 2.21 | 1,757 | 267 |
| Aug | 2.60 | 2,066 | 218 |
| Sep | 4.03 | 3,203 | 40 |
| Oct | 4.41 | 3,505 | |
| Nov | 2.69 | 2,138 | |
| Dec | 2.41 | 1,915 |
May is the wettest month (4.53 in, 3,600 gal off the roof); Feb the driest (1.73 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 San Marcos?
Best fit: 2 linked 55-gallon barrels, which delivers about 677 gallons to the garden in a normal year (88.4% 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 San Marcos's roof water will pass straight through it.
| Tank | Water used (gal/yr) | Spills over (gal/yr) |
|---|---|---|
| 55 gal | 592 | 27,708 |
| 110 gal | 677 | 27,624 |
| 165 gal | 677 | 27,624 |
| 275 gal | 677 | 27,624 |
| 550 gal | 677 | 27,624 |
| 1,000 gal | 677 | 27,624 |
| 1,500 gal | 677 | 27,624 |
| 2,500 gal | 677 | 27,624 |
| 5,000 gal | 677 | 27,624 |
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