First, and it beats everything below it
A silent leak undoes every efficiency measure in the house simultaneously.
A running toilet refills continuously, day and night, and it is frequently the largest single item on a water bill. Fixing it costs a few dollars for a flapper.
Test every toilet: a few drops of food colouring in the tank, no flushing, and check the bowl fifteen minutes later. Then run the meter test twice a year — shut off everything that uses water and see whether the meter still moves. Full method in finding a hidden leak.
This is not an upgrade, which is why it gets skipped. It is also the highest-return thing on this page by a wide margin.
Genuinely worth doing
Replace pre-1994 toilets. Three to five gallons per flush against 1.28 today, on the most-used fixture in the house. This is the largest single fixture saving available and it usually pays back quickly. Look for MaP testing figures rather than marketing — a low-flow toilet that needs two flushes has saved nothing.
Aerators. A few dollars each, fitted in minutes, and barely noticeable in use. The cheapest measure in plumbing.
Efficient showerheads. Showering is the largest indoor use after toilets. If yours has weak flow, descale it before replacing it — on our water that is usually the actual problem.
Insulate the first few feet of hot pipe leaving the water heater. Inexpensive, and it saves both water (less run-off waiting for hot) and the energy used to heat it. Hot water is two resources, which is why hot-side savings count twice.
Worth knowing
Every gallon of hot water saved is also the gas or electricity that would have heated it. That is why fixing a hot-side drip and insulating hot pipe outperform their cold-side equivalents, and why they are underrated on lists like this.
Good, but understand the trade-off
Heat pump (hybrid) water heaters are genuinely far more efficient than conventional electric, because they move heat rather than generating it. The catches are real though: they need a reasonable volume of air around them, they blow cold air out, and they are slower to recover. In a garage in a Texas summer the cooling side-effect is welcome; in a conditioned utility closet it is working against your air conditioning.
Tankless eliminates standby losses, which is a real saving, and lasts longer than a tank if maintained. But on 15-30 grain water that maintenance is not optional — a unit that never gets flushed can lose half its expected life. Choose it for endless hot water and longevity; treat the efficiency as a bonus rather than the business case.
Recirculation pumps save the water wasted waiting for hot to arrive, which in a large house is substantial. On a timer or demand control they are sensible; running continuously they burn more energy than the water is worth.
Frequently oversold here
Greywater systems. Attractive in principle. In practice they require permitting, ongoing maintenance, and a use case — and a Hill Country lawn's irrigation demand typically dwarfs the greywater a household actually produces. Worth investigating if you are already rebuilding; rarely worth retrofitting on the numbers alone.
Rainwater harvesting is the better regional bet and is well suited to this area, but it is a serious installation rather than a plumbing upgrade. If it ties into household plumbing it also creates a cross connection, which means a backflow assembly and annual testing.
Replacing working appliances for efficiency alone. The water and energy saved rarely justifies scrapping a functioning machine. Buy the efficient one when the old one dies — that is when the saving is real.
“Water saving” additives and gadgets that promise to descale or treat water without a softener. If it does not remove calcium and magnesium, it is not softening the water, whatever it is doing.
The Hill Country angle
Irrigation is the largest use in most homes here, often more than everything indoors combined in summer — and it is the least examined. Water before dawn, water deeply and less often, walk the system while it runs to catch broken heads, and adjust the controller seasonally. That single adjustment saves more than most indoor upgrades.
Check your drought restrictions. Boerne and surrounding systems set stages that limit irrigation days and times.
Size the softener correctly. Regeneration uses water, and an oversized or misconfigured unit regenerates far more often than it needs to. Correct sizing is a conservation measure as much as a salt-saving one.
Descale rather than replace. A showerhead cleaned in vinegar, an aerator soaked, a water heater flushed — all of these restore performance without manufacturing anything new, which is the least discussed and most genuinely environmental item on this page.