Treatment options for odor vary with the source and the concentration of the odor, so the first job is figuring out where it's coming from.

Aside from chlorine odors, most odors on municipally treated city water come from decaying organic material and algae in the source water. Other sources are decaying or contaminated distribution pipes, or the water heater in the home.

In well water, odors are commonly the result of sulfur bacteria, or compounds of iron, manganese, and sulfates. Hydrogen sulfide gas — the classic rotten-egg odor — occurs in well water as a result of decaying organic matter and the activity of sulfates and various species of sulfur or iron bacteria.

Determine the source: hot or cold water?

To eliminate the odor, first identify whether it's in the source water, or whether it's being created in your piping by bacteria or in the water heater by the anode rod.

Start outside. Run a hose bib and smell the cold water there. If the odor is present, your source water contains it, and you can likely treat the water as it flows into the house.

If you're on chlorinated city water and the outside hose bib has a strong chlorine odor, an activated carbon system will remove it.

If you have a rotten-egg or sulfur odor on city water, check whether it's only the hot water, or the cold as well — and whether the odor exists outside the house as well as inside.

If the odor is in the cold water inside the house only, one cause is old galvanized iron piping. Various strains of iron bacteria live in iron piping and give off methane and hydrogen sulfide gas as they decay.

Those same bacteria often thrive in water heaters — even new ones — as a result of the anode rod. For this problem, adding hydrogen peroxide (available at any drugstore) will eliminate it. This can be done by adding a special prefilter ahead of the water heater.

Let the water heater sit for several hours afterward. If the odor returns within days or weeks, the magnesium anode rod inside the heater needs replacing with a zinc-aluminum rod or an electric anode rod.

On city water with water heater odors? Our Water Heater Odor Killer is a simple, easy-to-attach spin-down filter system that solves it.

Rotten-egg odor in well water

Rotten-egg sulfur odors — and the black water that often accompanies them in hot and cold lines — come from the reaction of sulfates and microorganisms in water. Some well waters contain excessive sulfates along with various strains of sulfate bacteria. These bacteria are harmless to health, but they react in stagnant, oxygen-depleted water and produce hydrogen sulfide gas.

If your well water is used directly from the well and isn't aerated in an atmospheric (non-pressurized) storage tank, the odors are most likely from anaerobic bacteria. These thrive in oxygen-deprived environments, particularly in water high in sulfates.

If the cold water entering the home has no odor, the odor can still develop inside the home's cold piping, especially in galvanized iron. Iron piping in older homes is often corroded, which gives bacteria a good environment to grow in.

If there's odor in the cold water inside the home but not directly from the well, check whether the piping is iron and consider replacing it with copper. As a first step, shock-chlorinate and sanitize the piping to see whether that clears it.

Common methods to eliminate odors from well water

• Periodic shock chlorination with high doses of chlorine
• Aeration and filtration with catalytic activated carbon — Air-Charger sulfur filters, the most common choice for moderate sulfur odor with no chemicals to buy or mix
• Continuous ozone injection
• Continuous chlorine injection — effective on high odor levels and disinfects at the same time
• Continuous hydrogen peroxide injection — no chlorine taste, handles odor and iron together

Want more information?

Read our report: Eliminating Rotten Egg (Hydrogen Sulfide) Odors in Well Water Systems

Get complete well water testing, including bacteria, metals, and minerals: WaterCheck Tests