Why Does My Water Smell Like Rotten Eggs?

A sulfur, or rotten egg, smell coming from your faucet is unpleasant enough to make anyone worried, and understandably so. The good news is that it almost always has a specific, identifiable cause, and it's rarely a sign that your water itself is unsafe. Let's walk through what's actually happening.

First, Narrow Down the Source

The smell can point in different directions depending on where it shows up:

• Only from the hot water: this points strongly toward your water heater
• From both hot and cold water: this points more toward your water source, especially if you're on a private well
• Only in one particular fixture: could be an isolated issue with that drain or fixture, not your water supply at all

The Water Heater Explanation

The most common cause of a rotten egg smell, especially when it's only in hot water, is a reaction between naturally occurring sulfate-reducing bacteria in the water and the anode rod inside your water heater tank. Anode rods, often made of magnesium, are designed to sacrifice themselves to corrosion instead of letting your tank corrode, that's literally their job. But magnesium can react with certain bacteria to produce hydrogen sulfide gas, which is what creates that distinct sulfur smell.

This tends to happen more often in water heaters that sit unused for a while, in homes with well water, or in tanks with a magnesium anode specifically (as opposed to aluminum or zinc alloy versions).

A Simple Fix to Try

One commonly recommended approach is flushing the tank at a higher temperature, since heat can help disrupt the bacteria causing the reaction. This involves:

1. Turning the water heater thermostat up temporarily (electric units require shutting off power first, gas units can typically be adjusted at the control valve)
2. Letting the tank heat to the higher temperature for a couple of hours
3. Flushing the tank fully through the drain valve
4. Returning the thermostat to a normal, safe setting (120°F is the generally recommended setting for most households)

If the smell returns after this, replacing the anode rod, sometimes with an aluminum or zinc alloy version instead of magnesium, is often the more lasting fix.

The Well Water Explanation

If the smell is present in both hot and cold water throughout the house, the cause is more likely related to your water source itself rather than the water heater. Well water in particular can pick up hydrogen sulfide gas from decaying organic matter or bacteria naturally present in groundwater. This typically calls for water testing to understand exactly what's present and whether treatment, like an aeration or filtration system, is needed.

Is It Safe?

For most households, the rotten egg smell caused by anode rod reactions or naturally occurring sulfur bacteria is unpleasant but not a direct health hazard at typical household concentrations. That said, hydrogen sulfide gas at high concentrations can be dangerous, and any strong, persistent sulfur or gas-like smell in an enclosed space deserves caution rather than assumption. If the smell is strong, sudden, or accompanied by any other symptoms like headaches or dizziness, ventilate the area and treat it seriously rather than waiting it out.

When to Get Help

A rotten egg smell that persists after flushing the tank, or that shows up in both hot and cold water suggesting a source-level issue, is worth having professionally diagnosed rather than guessed at repeatedly. ProFlow Plumbing can test your water, inspect your water heater's anode rod, and recommend the right fix so you're not just masking the smell every few weeks.