If the hot tap in your Arnold home smells like rotten eggs, or like something metallic or swampy, while the cold tap smells fine, the cause is often inside the water heater rather than in the supply coming into the house. That split matters. It tells you where to look first and keeps you from buying equipment for a problem you may not have.
Start with the pattern
Before you touch anything, write down what you notice:
- Does the smell appear only at hot taps, or at both hot and cold?
- Did it start after a change in water source, a new heater, or a long stretch away from home?
- Does running the water clear it, or does the smell come back?
- Is your home on the public system or a private well?
A smell on the hot side only points toward the heater, its anode rod, or the hot line. A smell at both taps points toward the supply itself, which in a private well may mean hydrogen sulfide or bacterial activity in the well or pressure tank. Public water in Arnold is treated with chloramine, which can have a mild chlorine-like smell. That is a different odor from sulfur, so keep the two separate when you describe what you smell.
What the heater can do to water
Most storage water heaters have a sacrificial anode rod, usually made of magnesium or aluminum, that draws corrosion away from the tank wall. In some water, bacteria inside the tank can react with the anode and produce hydrogen sulfide, which gives a sulfur smell that shows up at the hot tap only. Heat also speeds up many chemical reactions, so water that smells fine cold may smell off once it has been heated.
Checks you can make safely
- Run the cold tap for a minute, then smell it. If the cold water is clean, the supply is probably not the source.
- Run the hot tap for a minute, then smell it at the sink. Write down the result.
- Note the thermostat setting on the heater without changing it. Check the age of the unit and any service records you have.
- Before opening any panel, turn off power or gas and follow the manufacturer's manual for the unit.
- If you have a private well, collect samples from both taps for a laboratory test before you make repairs.
Anode rod and flushing
Inspecting the anode rod means shutting off power or gas, closing the cold supply, and draining enough water to slide the rod out of its port. A rod that is heavily coated or mostly corroded has been doing its job. Replacing a spent rod is a common maintenance step, but if you are not comfortable working near gas or high-voltage connections, have a licensed plumber or heating technician do it. Let the water cool before draining, and follow local code for where the drained water can go.
When the smell is in the well
If you draw from a well, the smell may come from the well itself. Hydrogen sulfide and sulfate are common in private wells in this part of Jefferson County, and iron or manganese can add staining. A sulfur smell at both taps points to the well, not the heater. A laboratory test is the only reliable way to know which substances are present.
A note for south and west Arnold well owners
Well owners in the south and west parts of the Arnold area should sample their water for lead. EPA is actively addressing lead and other heavy metals in private wells tied to the Southwest Jefferson County Mining Superfund area. Lead has no smell or taste, so a sulfur-smelling sample will not tell you whether lead is present. Ask the lab for a lead test, and keep those results with your other water records.
When to call for help
Call a plumber or heating technician if the heater is leaking, the tank is past its expected service life, or you smell gas at any point. If the sulfur smell persists at both taps on a private well, contact a certified laboratory and ask about a sulfide test and a basic coliform check. Keep notes on when you first noticed the smell and any changes to the system. Those notes help whoever tests or repairs your water system choose the right next step.