A rotten-egg smell at the faucet can come from the water, the drain, or—in a very different emergency—the gas system in the room. Start by identifying exactly where the odor exists. If the smell is only in running hot water and follows you to several fixtures, the water heater becomes a strong suspect. If hot and cold both smell, the incoming water supply deserves attention first. If the room itself smells like leaking gas, do not continue the faucet test.
Before you continue, check these safety points.
- If you smell or hear leaking gas in the room, leave immediately and contact the gas utility or emergency services from outside; do not operate electrical switches or phones before leaving.
- Hot-water tanks can contain scalding water and stored pressure; isolate energy and water according to the manufacturer's procedure before any service work.
- Do not add household chemicals to a water heater or remove its sacrificial anode as an improvised fix; use an approved treatment procedure or qualified service.
First separate water odor from a gas leak or a smelly drain
Fill a clean glass with water and move away from the sink before smelling it. If the glass smells normal but the sink area smells bad, the drain or overflow may be the source. If the room itself has a strong gas-like odor, you hear gas leaking, or the smell is present even when no water is running, leave immediately and contact the gas utility or emergency services from outside; do not operate switches or phones before leaving.
Only continue water troubleshooting when the odor clearly follows the water itself. A simple hot-versus-cold comparison at two or three fixtures is more useful than immediately flushing the heater or replacing an anode.
Hot-only odor points toward the water heater; hot-and-cold odor points upstream
Run cold water into one clean glass and hot water into another, then compare them away from the drain. Repeat at another fixture. If only the hot water has the odor, conditions inside the water heater may be supporting the problem. If both hot and cold smell, investigate the municipal or private-well supply, treatment equipment, and plumbing before modifying the heater.
A. O. Smith identifies sulfate-reducing bacteria as a common cause of smelly water in water heaters. Those bacteria can convert sulfate into hydrogen sulfide gas, which creates the characteristic rotten-egg odor, and the tank's chemistry can influence the problem.
Do not remove the anode rod just because the odor involves sulfur
The sacrificial anode is there to protect a steel tank from corrosion. Some odor problems can involve interactions among water chemistry, bacteria, and anode material, but permanently removing corrosion protection can shorten tank life and may conflict with manufacturer requirements or warranty terms.
If the manufacturer recommends an alternate anode material or powered anode for your water conditions, compatibility must be checked by model. Replacement can also require substantial torque and safe isolation of hot water, electricity, or gas, so it is often better handled by a plumber or qualified water-heater technician.
Flushing or sanitizing is not a casual chemical experiment
Manufacturer technical bulletins may use tank flushing or controlled chlorination as part of odor correction, especially when bacteria are involved. The exact procedure depends on heater design, water source, plumbing materials, and whether the home has treatment equipment.
Do not pour bleach, peroxide, acids, or other chemicals into a water heater without a procedure approved for that system. Incorrect concentration, mixing, or incomplete flushing can create chemical exposure, damage equipment, or leave unsafe water in the plumbing.
Private-well homes may need a water-quality answer, not just a heater repair
If sulfur odor occurs in both hot and cold water, returns quickly after heater service, or changes with well pumping and treatment cycles, test the source water through an appropriate local laboratory or water professional. Hydrogen sulfide, sulfate, iron bacteria, and other water-quality conditions can require different treatment approaches.
For renters, report persistent hot-water odor to property management with the hot-versus-cold comparison instead of altering the water heater. For homeowners, bring the heater model and water-source information to the service call so the fix is matched to the actual system rather than guessed from odor alone.
Before you call it done
- The odor was confirmed in a glass of water rather than only at the drain or in the room.
- Hot and cold water were compared at more than one fixture to distinguish a heater issue from a source-water issue.
- A gas-like room odor or audible gas leak is being treated as an emergency, not as a water-heater odor diagnosis.
- The anode has not been removed or substituted without checking heater compatibility and corrosion protection requirements.
- Any flushing, disinfection, anode change, or water treatment is being matched to the heater model and actual water source.