Understanding GPM in Context
Gallons per minute (GPM) is the standard measure of water well yield — how much water the well can produce over a sustained pumping period. The "right" number depends entirely on what you need the water for. A number that is perfectly adequate for a weekend cabin is inadequate for a 50-head cattle operation.
Residential use
A typical rural house in Blanco County uses 50–100 gallons of water per person per day for household purposes — showers, toilets, laundry, cooking. A family of four consuming 400 gallons per day needs a well that can deliver that volume reliably. At 1 GPM (1,440 gallons per day theoretical maximum), a well could supply a family of four — but 1 GPM is the absolute floor, and in practice, wells tested at 1 GPM frequently produce less under real-world pumping conditions. A properly sized storage tank (2,000–5,000 gallons) provides a buffer against low-yield wells, allowing the well to recharge overnight and supply peak demand during the day.
Livestock operations
Cattle require approximately 30–50 gallons per head per day in warm weather. A property running 20 head of cattle needs 600–1,000 gallons per day of water — already double what a single household uses. At 3 GPM (4,320 gallons per day theoretical maximum), a well can support modest livestock operations alongside household use. Higher stocking rates require either a higher-yield well, multiple wells, or storage infrastructure that allows the well to run continuously and accumulate volume.
Irrigation
Irrigating even a small garden or food plot requires substantially more water than household use — a single acre of lawn or pasture at moderate application rates can require 20,000–30,000 gallons per acre per week during Texas summers. For serious irrigation purposes, well yield requirements jump to 10–50+ GPM, and many Blanco County wells cannot support meaningful irrigation. Buyers planning agricultural irrigation should verify yield carefully and consider the economics of irrigation at Blanco County water depths.
The Reliability Question
Driller-reported yield estimates on well logs reflect conditions at the time of drilling — which may be decades ago. Static water levels and actual yield can change with drought conditions, increased regional pumping, and aquifer depletion. The most relevant data for a purchase decision is current performance, not the original log estimate. A pump test (typically a 4-hour step drawdown test) measures actual yield under current conditions and is the appropriate standard for due diligence on any property where water supply is critical.
