Stinky Water: Why Does My Tap Smell Like Rotten Eggs?

The Smell Comes From Sulfur, But What Causes It?

The rotten egg smell in tap water usually means you’re dealing with hydrogen sulfide gas, which is produced when sulfur-reducing bacteria break down organic matter in low-oxygen environments, like wells, plumbing systems, or municipal water lines. These bacteria aren’t necessarily dangerous on their own, but their byproducts can lead to more serious concerns. Hydrogen sulfide is most noticeable when you turn on the hot water because many water heaters with magnesium anode rods create the perfect environment for these bacteria to thrive. When water sits in the tank and the temperature drops slightly, it encourages the growth of sulfur-reducing bacteria. The smell intensifies with heat, so you may not notice it in the cold tap at all. If you use well water, the problem might be in the source itself. Groundwater picks up naturally occurring sulfates, and bacteria in the well convert those into hydrogen sulfide. Professionals with experience in well systems can run a simple water test to check for these compounds and determine the origin of the problem. If you’re on city water and the smell appears suddenly, it could be from a corroded pipe, a break in the system, or stagnant water in an underused line. In these cases, a plumbing repair service might be your best bet.

How to Narrow Down the Source of the Smell

To fix the problem, you first need to pinpoint where it’s coming from, so check whether the smell is in all your faucets or just one, whether it’s in the hot water only, and whether it comes from both indoor and outdoor taps. If the smell is only in hot water, the culprit is almost certainly your water heater. That doesn’t always mean the unit is broken. It may need cleaning or an anode rod replacement. A plumber in Corona, CA can flush the tank, disinfect the interior, and install a zinc or aluminum anode rod instead of the magnesium one that feeds the bacteria. If the smell is in hot and cold water, and throughout your whole house, it’s likely coming from the source water. For private wells, testing for sulfur bacteria, iron bacteria, and other contaminants is the best first step. Some well owners install aeration systems, activated carbon filters, or chlorination systems to eliminate the problem at its source. If the smell is only in one faucet, the problem might be localized to the sink's drain or plumbing line. Organic matter caught in the drain or P-trap can decay and cause odors that get released when water flows through. Cleaning the drain can usually resolve this issue. If the smell appears after long periods of non-use, like in guest bathrooms, outdoor spigots, or seasonal cabins, it may just be stagnant water. Flushing the lines can help, but you should still check with a pro to rule out deeper issues if the smell doesn’t go away.