If your well water smells like rotten eggs, you are smelling hydrogen sulfide gas, and where you smell it tells you where it is coming from. If only the hot water smells, the usual culprit is the magnesium anode rod inside your water heater feeding sulfate-reducing bacteria in the tank. If every tap smells, hot and cold alike, the sulfide is in the well itself, produced by bacteria in the aquifer or the well casing. The fixes are completely different: an anode swap or a tank flush for the first, and aeration, oxidizing filtration or chlorination for the second. That is why the first rule of a sulfur smell is to diagnose before you buy anything.
We have treated Hill Country well water from Spicewood since 2003, and the rotten-egg question peaks every summer as wells draw down. Here is how we sort it out.
Hot water only vs. every tap: the two-minute diagnosis
You can narrow this down at the kitchen sink before anyone shows up.
- Run the cold tap for two full minutes to clear the water sitting in the pipes, then fill a glass and smell it immediately. Hydrogen sulfide is a gas and leaves the water quickly, so smell at the tap, not across the room.
- Run the hot tap for two minutes and smell that.
- If you have a softener or an RO faucet, smell the softened tap and the drinking-water faucet too, then compare them with an unsoftened outdoor hose bib, which is your raw water.
Read the results this way:
- Hot smells, cold does not. The problem is inside the water heater. Skip to the anode section.
- Both smell, and the hose bib smells too. The sulfide is coming up the well. That is a treatment problem.
- Softened water smells but raw water does not, or smells noticeably worse. The softener resin bed or brine tank has become a home for sulfur bacteria. It needs sanitizing, and the well probably needs treatment ahead of it.
- Smell only first thing in the morning or after a trip, then it fades. Stagnant water in the lines or the heater. Bacteria growing in the plumbing, not necessarily the aquifer.
One more clue: tankless heaters have no anode rod. If your hot water smells and the heater is tankless, the sulfide is in the well and the heat just makes it easier to smell.
Why Hill Country wells carry sulfur
Hill Country well water comes out of limestone and dolomite, and sulfur rides along with it. Wells around Johnson City, Round Mountain, Blanco and the Pedernales corridor draw from two aquifers: the Ellenburger-San Saba, a fractured dolomite the Blanco-Pedernales Groundwater Conservation District describes as "inherently hard," and the Trinity Group (Glen Rose limestone, Hensell sand, Cow Creek), whose Upper Glen Rose beds contain gypsum. Gypsum is calcium sulfate, and when sulfate-rich water sits in an oxygen-free aquifer, sulfate-reducing bacteria turn that sulfate into hydrogen sulfide.
The numbers back this up. The USGS/TWDB groundwater survey of Blanco County found sulfate above 250 mg/L (the federal secondary limit for taste) in 18 percent of 521 well samples, with readings as high as 2,900 mg/L, and BPGCD's management plan flags the Middle Trinity specifically for "hardness and odors." A 433-foot Trinity well south of Johnson City sampled by the USGS in 2021 tested 1,640 mg/L sulfate, 1,940 mg/L hardness and 2,830 mg/L total dissolved solids. Water like that does not just smell; it is bitter, it scales everything, and it fouls softener resin. The same survey found iron above 0.3 mg/L in 45 percent of samples, and iron bacteria, the ones that leave orange slime in the toilet tank, often live alongside sulfur bacteria and add their own musty, swampy odor.
Drought makes all of it worse. Blanco County has been under a BPGCD drought stage continuously since August 2022, reaching Stage 4 (Critical) before easing to Stage 3 in April 2026 and Stage 2 in July 2026. When static levels fall, pumps pull deeper, older, lower-oxygen water; wells cycle more and sit stagnant longer between cycles; and a Johnson City driller lists the classic drought trio of air-spitting taps, short-cycling pumps and water that turns cloudy or smelly. Trinity wells around Dripping Springs have been dropping too, with a local driller reporting static levels near 660 to 690 feet against roughly 500 feet historically, and the Glen Rose evaporites there raise magnesium and sulfate. Hydrogen sulfide is less documented on the Hays County side, so there we test rather than assume.
The water-heater anode reaction
If only the hot water smells, your water heater is manufacturing the smell. Every glass-lined tank heater has a sacrificial anode rod, usually magnesium, that corrodes so the steel tank does not. As the magnesium gives up electrons, it creates exactly the conditions sulfate-reducing bacteria want: a warm tank, sulfate in the water, and a ready supply of electrons to convert that sulfate into hydrogen sulfide. The smell is strongest in the morning, after the water has sat in the tank overnight.
Options, in the order we suggest them:
- Flush the tank. Drain it, refill it, and see whether the smell returns. If it comes right back, flushing alone will not hold.
- Swap the anode. An aluminum-zinc anode does the same corrosion-protection job with far less of the electron donation that feeds the bacteria. This is the single most common fix for a hot-only smell, and it is a plumber-level job, not a treatment-system job.
- Go powered. An impressed-current (powered) anode protects the tank electrically and never corrodes, so there is nothing for the bacteria to feed on. It costs more up front and lasts the life of the heater.
- Temporary heat. Sulfate reducers thrive around the 120F most heaters are set to. Raising the tank to 130-140F for a few hours and flushing can knock them back, but the effect is short-lived and raises scald risk, so treat it as a stopgap, not a fix.
What we do not recommend is pulling the anode out entirely. Without it the tank rusts through early, and on very hard Hill Country water the tank is already fighting scale.
If the heater fix works but the smell drifts back over a few months, sulfate and sulfur bacteria in the well water are reseeding the tank, and it is time to look upstream.
How to get rid of the sulfur smell in well water
When every tap smells, the fix belongs at the wellhead or the point of entry, and it starts with a test. Hydrogen sulfide is a dissolved gas that escapes a sample bottle within hours, so it is measured on site, along with iron, manganese, pH, sulfate and hardness, because the right treatment depends on how much sulfide there is and what is riding with it. Every system we recommend starts with that test; what we measure and how is on our water testing page.
From there, sulfide treatment scales with the load:
- Low levels: catalytic carbon. A catalytic activated-carbon tank oxidizes and adsorbs small amounts of hydrogen sulfide with no chemicals. It is quiet and low-maintenance, but it is overwhelmed by heavy sulfide or significant iron.
- Moderate levels: air-injection oxidizing filter. A single-tank system draws in air, oxidizes dissolved sulfide (plus iron and manganese) into solid particles, traps them in a media bed and backwashes them to drain. This is the workhorse for most sulfur and iron problems on Hill Country wells, and it is the core of our iron and sulfur removal service.
- Heavy loads or bacteria: chlorination, retention, filtration. A feed pump injects chlorine, a retention tank gives it contact time to oxidize the sulfide and kill sulfur and iron bacteria, and a carbon filter removes the chlorine and the precipitate before the water reaches the house. More equipment and more maintenance, but it handles wells nothing else will.
- Bacteria in the casing: shock chlorination. If sulfur or iron bacteria have colonized the well itself, a one-time shock of the casing and pressure tank is the starting point. It often quiets a mild smell for months, but it is not permanent if the aquifer keeps supplying sulfate.
Because sulfide rarely shows up alone out here, most Blanco County systems end up as part of a larger package: sediment, oxidizer, softener, and often reverse osmosis for sulfate and TDS at the kitchen tap. That whole-well approach is covered on our well water treatment and filtration page.
Why a softener alone makes it worse
A water softener will not remove a rotten-egg smell, and it can make the problem worse. Softener resin exchanges calcium and magnesium ions; hydrogen sulfide is a dissolved gas, not a hardness ion, so it passes straight through. Meanwhile sulfide and iron coat the resin beads and cut capacity, and the warm, low-oxygen brine tank is a comfortable place for sulfur bacteria to grow. Homeowners who install a softener to "fix the smell" often end up with a smell at the softened taps and a softener that has stopped softening.
The right order is oxidizer first, then softener. Once the sulfide and iron are out, a demand-initiated water softener sized for the remaining hardness can do its job and stay clean. On a septic lot, demand-initiated regeneration is also what Texas law requires.
When it's a warning sign, not just a smell
At the levels found in household wells, hydrogen sulfide is a nuisance, not a health hazard; the nose detects it long before concentrations reach anything dangerous. It is not harmless to the house, though. It corrodes copper, brass and steel, blackens silverware, and shortens the life of heater elements and pump parts. And it can be a flag for something that does matter:
- A sudden new smell, especially after heavy rain, can mean surface water is reaching the well. The July 2025 Central Texas floods and the July 2026 Pedernales flood, which pushed the river near Johnson City to its highest level since 1979, put wellheads under water along the Pedernales in Blanco County. Any flooded or newly smelly well should get a coliform and E. coli test. A positive result means boil-water guidance and a scheduled visit for disinfection or a UV system, which we cover on our water purification page.
- Rising odor plus falling pressure usually means sulfur or iron bacteria slime is clogging the pump intake, screens or pressure tank. That is a well-service problem as much as a treatment problem.
- Cloudy or sandy water with the smell usually means the pump is pulling near the bottom of a drawn-down well.
Texas does not regulate private wells; testing is the owner's job, and TCEQ recommends an annual bacteria and nitrate test. The Texas Well Owner Network runs low-cost screenings in Johnson City periodically, and we test on site as the first step of any treatment recommendation.
Sulfur wells in Blanco County: where to start
Around Johnson City, the pattern is predictable: Ellenburger wells near town run very hard and can carry radon, while the Trinity wells south and east toward Blanco, Hye and Pedernales Falls carry the gypsum sulfate and the rotten-egg smell. The same Glen Rose chemistry follows US-281 north through Round Mountain and, with less documented sulfide, into the Trinity country around Dripping Springs. Every well in Blanco County is registered with BPGCD, new lots must be at least five acres for a well and septic, and the aquifer has been drawn down through four years of drought stages.
Absolute Water Solutions LC is based in Spicewood and has treated Hill Country well water since 2003. We are TCEQ-licensed (WT001370) and insured, and every job is done by our own crews. Run the two-minute test above. If only the hot water smells, call a plumber about the anode. If every tap smells, call us at (512) 587-8188 during business hours, Monday through Friday, 8am to 5pm, or request a free estimate. We will test the water, tell you honestly whether it is the anode, the well or both, and size the system to what the test actually shows.