Hot water smells like rotten eggs: what to check

When hot water smells like rotten eggs but cold water does not, the water heater is a useful starting point for diagnosis. Hydrogen sulfide can develop through sulfur bacteria or reactions involving water and the tank's anode; the odor alone does not identify a failed part, according to the Minnesota Department of Health's source-finding guide.

Start with where the smell occurs, rather than buying a replacement anode or treatment system. Write down which taps are affected, whether the problem is new, and whether equipment was recently serviced. These details help the plumber narrow down the source.

Separate water odor from a suspected gas leak

An odor in the room or near gas equipment needs a different response from a complaint limited to water at a tap. If you smell natural gas or suspect a gas leak, leave immediately and call SoCalGas at 1-800-427-2200 from a safe location. Call 911 if the leak threatens life or property, or you cannot reach SoCalGas. Avoid switches, flames and devices that could spark, and do not attempt repairs. Do not continue checking faucets to prove the smell is water-related when a gas leak is suspected.

For a water-only complaint, describe what you have already noticed during ordinary use. Do you notice it at the kitchen sink, bathroom sink and shower, or only one location? Does cold water have the same odor? The Minnesota guide uses the hot-versus-cold distinction to help narrow the investigation. Its well-water treatment discussion is not evidence that an Orange County public supply has the same issue.

Why the heater and water chemistry matter

A. O. Smith's Bulletin 22 describes hydrogen sulfide associated with sulfur bacteria and conditions inside the water system. It identifies long periods without water movement and water softeners among factors that can increase the potential for odor. That is a reason to report a recent absence or treatment change, not a diagnosis of your home's water.

Bring the heater model, water supplier and treatment-equipment names to the discussion. If the smell started after a softener installation or filter service, include that date. If it was first noticed after the home stood unused, say how long the home was empty. Avoid changing several pieces of equipment before the source has been established.

The water-supplier identification guide can help you find the right local report and contact. Use the supplier that actually serves the address. A countywide assumption about hardness does not establish the chemistry inside a particular heater.

What an anode does, and what it cannot prove

Understanding the anode helps frame that discussion. In the A. O. Smith 300/301-series manual, page 53, sacrificial anodes protect the glass-lined tank from corrosion and gradually deplete. The manual also discusses powered anodes as a separate design. These are model-specific components, not interchangeable remedies selected by smell alone.

Ask the service professional to identify the anode design in your heater and check manufacturer-supported options. An alternative rod may be worth discussing when the investigation supports an anode-related odor, but removing corrosion protection is not an appropriate shortcut. The same manual warns against permanent removal and says a special anode may reduce, rather than eliminate, an odor problem.

The manual applies to the heater families listed on its cover. It is not an installation instruction for your heater unless its model matches. Keep that distinction when comparing a powered anode rod with magnesium or another sacrificial material: ask for the correct part reference and manufacturer guidance before authorizing a change.

Discuss options without treating every odor alike

A. O. Smith Canada's powered-anode explanation describes how its system addresses an anode-related sulfate reaction. That supports discussing the technology; it does not establish compatibility with every heater or promise that every rotten-egg smell will disappear. A useful proposal should explain what evidence points to the anode and which manufacturer instructions support the proposed part.

Ask whether the investigation points to the heater, treatment equipment or incoming water. Request a clear explanation of any proposed water testing and what the result would change. If an odor treatment is recommended, ask who will perform it and how the result will be checked afterward.

Do not add peroxide or other chemicals, turn up the temperature to treat the smell, drain the heater, or remove an anode yourself. The Minnesota guidance warns that elevated-temperature treatment can cause scalding and advises professional help for heater work. Its treatment procedures require more context than a homeowner odor checklist provides.

Prepare a useful service request

Keep the request specific. Instead of asking for an anode replacement immediately, report “odor at several hot taps, cold water unaffected” if that matches what you observed. Include:

• The affected fixtures and when the odor was first noticed.
• Whether it occurs during ordinary hot-water use, cold-water use, or independently of running water.
• The heater model and any safely visible message or fault code.
• The supplier name and any softener or filtration equipment.
• Recent service, equipment changes or periods when the home was unused.

Keep any water-test results and the exact replacement-anode part number with the service record. You do not need to open the heater or enter an enclosed equipment space to collect a useful history.

If replacement is proposed, our repair-or-replace guide covers that separate decision. This odor guide does not establish that the tank needs replacement or that the water is safe to use. Direct water-quality concerns to the supplier or an appropriate testing professional.

Common questions