Rotten Egg Smell in Well Water

Hot water only, or hot and cold?

This one test sorts out most cases.

Smell only in the hot water. Penn State says the water heater is the likely source. The magnesium anode rod, there to stop the tank rusting, can react with sulfate in the water and turn it into hydrogen sulfide. Water that sits in the tank for days, like after a vacation, often smells worst.

Smell in both hot and cold. The hydrogen sulfide is in the water coming from the well. That's usually sulfur-reducing bacteria, which live naturally in groundwater and thrive in low-oxygen places like wells and plumbing. Penn State says it's most common in wells drilled into shale and sandstone.

Smell only from softened taps. Rare, but Penn State notes a softener can create conditions that let sulfur bacteria grow. Sanitizing the softener per its manual is the place to start. See water softener maintenance.

Smell only for a few seconds when you first open a tap. Often a drain, not the water. Run the water into a glass, step away from the sink and smell the glass.

Is it safe to drink?

Usually yes, at the levels you'd find in a home well, but nobody wants to. Most people can smell hydrogen sulfide well below 0.5 mg/L, and Penn State says there's no drinking water standard for it because water becomes undrinkable from the smell before it reaches harmful levels. The bacteria themselves aren't a health concern.

The bigger costs are to the house. Hydrogen sulfide corrodes metal plumbing and leaves yellow or black stains on fixtures. It also tarnishes silverware and can turn coffee and tea off.

A sudden new smell is still worth a test. The CDC says to test your well whenever its taste, color or smell changes, because a change can point to contamination.

Water heater fix: replace the anode rod

Penn State's fix is to replace the magnesium rod with an aluminum one, which should end the odor and still protect the tank. Don't just pull the rod and leave it out. That speeds up corrosion, shortens the heater's life and likely voids the warranty.

Anode rods are often seized tight, so you may need a long breaker bar and a helper holding the tank. If there's no headroom above the heater, a flexible link-style rod fits. Step-by-step: water heater anode rod replacement. For the full water heater side of this problem, see water heater rotten egg smell.

Testing for hydrogen sulfide

Hydrogen sulfide escapes from a sample quickly, so Penn State says to test it in the home, or chemically stabilize the sample before it goes to a lab. Use a state-accredited lab, and call first to ask whether it tests for hydrogen sulfide and what bottle to use.

Order iron and manganese on the same sample. NDSU notes hydrogen sulfide often shows up alongside them, and the treatment choice depends on all three. A sulfate test also helps on the water heater side, since EPA's secondary limit for sulfate is 250 mg/L and the anode reaction feeds on it.

How to get rid of sulfur smell in well water

Pick the treatment by how much hydrogen sulfide you have. These are Penn State's ranges:

For a low, steady smell with no iron problem, a whole-house carbon or catalytic carbon filter is the simplest system to own. If you also have iron or manganese, an oxidizing filter or a chlorine feed handles all of it at once. See whole house water filters for well water to compare setups.

Shock chlorination first

When the cause is sulfur bacteria, shock chlorination is often the first step: chlorine goes straight into the well to kill the bacteria. The catch is that the smell usually comes back quickly as the bacteria recolonize. If the relief is too short-lived, Penn State says to consider a continuous treatment system. Instructions: how to shock chlorinate a well.