Rotten-egg smell only from hot water? The water heater anode rod fix

Sources last checked: October 31, 2026

If the cold water is fine and only the hot water smells like rotten eggs, the Florida Department of Health says the problem “likely is in the water heater.”¹

Why it happens

• Water heaters come with a magnesium rod (the “anode”) that protects the tank from corrosion.²
• Penn State Extension explains that the magnesium rod “can chemically reduce sulfates to form hydrogen sulfide,” the rotten-egg gas.²
• FL DOH also notes that “chemical reactions inside water heaters” can be a source.¹

The fix Penn State Extension describes

Before you start

1. Confirm it’s hot-only. Run the cold tap and smell it. If the cold water smells too, the source is more likely the well, the plumbing or a softener. Use the diagnosis guide.¹
2. Check your warranty and manual. See whether your heater’s manufacturer allows anode swaps and which rod type it specifies. (Our advice: if you’re not comfortable working on a water heater, hire a licensed plumber.)
3. Gas or electric, shut off power/fuel and water first. This is standard safety practice. Follow your manufacturer’s manual.

If the smell comes back

If the hot-water smell persists after the swap, or the cold water starts to smell too, you may have sulfur bacteria in the well or plumbing, or H2S in the groundwater. Shock chlorination and testing are the next steps.^{1 2}

Sources