Well Water Smells Like Rotten Eggs? Here's How to Find the Cause

A rotten egg or sulfur smell is the most common bad-odor complaint from well owners, according to the Texas Well Owner Network run by Texas A&M AgriLife. The smell comes from hydrogen sulfide gas. The good news is that a simple test at your faucets usually tells you where it's coming from, and that points you to the right fix.

Step 1: Hot Tap or Both Taps?

Run the cold water at a faucet, then the hot water, and smell each one.

• Only the hot water smells. The source is almost always your water heater.
• Both hot and cold smell. The source is more likely the well, the storage or pressure tank, or the groundwater itself.

If Only the Hot Water Smells

Most tank water heaters have a metal rod inside called an anode, usually made of magnesium, which protects the tank from rusting. When well water contains sulfate, the anode can help turn that sulfate into hydrogen sulfide gas, and the warm tank is a good home for the bacteria involved.

Common fixes, according to Texas A&M AgriLife and other university extension services:

• Replace the anode. A plumber can swap the magnesium anode for an aluminum or other type made for this problem. Simply removing it is not recommended, because the tank can corrode faster and the warranty may be voided.
• Disinfect and flush the water heater. This can kill the bacteria, though the smell may come back.

Leave water heater work to a plumber unless you're experienced. High temperatures and pressure can cause serious burns.

If Both Hot and Cold Water Smell

When every tap smells, bacteria in the well or tank, or naturally occurring sulfide in the groundwater, is the likely source. Texas A&M AgriLife's well owner program suggests:

• Shock chlorination by a licensed pump installer or well driller. This kills bacteria in the well and plumbing. It often helps, but it isn't a permanent fix, because the bacteria and the sulfur source occur naturally and the odor can return.
• A treatment system for lasting control. An activated carbon filter can handle low levels of hydrogen sulfide. Higher levels usually need an oxidizing filter, such as manganese greensand.

Why Hill Country Wells Get This

Many wells around Bulverde, Spring Branch, Boerne, and Canyon Lake draw from the Trinity Aquifer. Texas Water Development Board groundwater studies have linked high sulfate in some Hill Country wells to gypsum-bearing layers in the upper Glen Rose limestone. Sulfate itself has no smell, but it's the raw material the water heater anode and sulfur bacteria turn into hydrogen sulfide.

Get the Water Tested First

Before buying treatment equipment, test the water so you treat the actual problem. Ask the lab for sulfate and hydrogen sulfide along with the usual bacteria test. Hydrogen sulfide escapes quickly from a sample, so follow the lab's collection instructions closely. See our well water testing page for more on testing options.

When to Call a Pro Right Away

• The smell started suddenly along with cloudy, discolored, or bad-tasting water
• You also notice a fuel, chemical, or sewage odor, which is not normal and calls for testing before drinking
• Low pressure, sputtering, or the pump running constantly

FAQ

Is rotten egg smelling well water safe to drink? The sulfur bacteria themselves aren't considered a health risk, and low levels of hydrogen sulfide are mainly a taste and odor problem. But a smell can hide other issues, so have the water tested, especially if it's new or changed suddenly.

Will a water softener fix the smell? No. A softener is not designed to remove hydrogen sulfide, and in rare cases a softener can give sulfur bacteria a place to grow.

Why did the smell come back after the well was shocked? The bacteria and sulfur source occur naturally, so shock chlorination is usually temporary. A treatment system is the long-term option.

Get Help From a Local Well Pro

If both taps smell or you want the well shocked or tested, request a free quote and we'll pass your request to an independent, licensed local well professional who serves your area.

Sources: Texas Well Owner Network (Texas A&M AgriLife) FAQ; "Hydrogen Sulfide in Drinking Water: Causes and Treatment Alternatives" (Texas A&M AgriLife); Penn State Extension; Minnesota Department of Health; Texas Water Development Board groundwater reports. This page is general information, not a substitute for a water test or a professional's advice.