Three Droughts, No Well: A Rainwater-Only Homestead in the Texas Hill Country

Two neighbors on their road drilled deep and came up dry. A third hit water at 620 feet that tested high in sulfate. When the Alvarezes got their own quote — $34,000, no guarantee — they started measuring their roof instead.

The math surprised them. At 32 inches of average rainfall, 3,100 square feet of metal roof sheds about 62,000 gallons a year. A household of four using 45 gallons a day needs roughly 66,000. Add the barn roof and the supply side was solved on paper before anyone dug a hole.

The real design work was the gap, not the total. Hill country rain arrives in violent spring and autumn bursts with long dry stretches between. We sized storage against a 71-day dry period from the historical record rather than the annual average, which is how 30,000 gallons became the number.

Treatment was where they refused to economize. Dual first-flush diverters dump the first twelve gallons off every downspout, and the potable chain runs sediment, carbon and UV with a lab test each spring and fall. Five years of results have come back clean.

The overflow turned out to be a bonus. Instead of piping excess to the road, they cut two swales above the orchard. Nineteen fruit trees have never been irrigated from the tanks — they drink what the tanks cannot hold.

What we'd do differently

• Size storage against your longest historical dry gap, not annual rainfall. The gap is what empties a tank.
• First-flush diverters are the cheapest water-quality improvement available. Put one on every downspout, not just the main one.
• Buy tanks in multiples. Three tanks let you isolate one for cleaning or repair without losing the supply.
• Plumb the overflow somewhere useful before the first big storm. Their original overflow washed out a driveway culvert in month two.
• Test twice a year even when it tastes fine. The spring test is the one that catches roof and gutter problems.