Why Does My Water Smell Like Rotten Eggs in Ohio?

Why does my water smell like rotten eggs?

That smell is hydrogen sulfide gas dissolved in your water. You do not need much of it to notice. Ohio State's Ohio Watershed Network puts the taste threshold at 0.05 ppm and the smell threshold at 0.1 ppm, so a strong odor does not mean a high concentration.

In practice, three things cause it:

1. **The groundwater itself.** The gas is already in the aquifer before the water reaches your well. 2. **Sulfur bacteria.** Bacteria living in your well, your pressure tank, your softener or your plumbing feed on sulfate that is naturally in the water and give off the gas as a byproduct. 3. **Your water heater.** The magnesium anode rod inside the tank converts sulfate in the water into hydrogen sulfide.

All three look identical at the faucet and have completely different fixes. One of them is a forty dollar part. Figure out which one you have before anyone sells you equipment.

Is water that smells like rotten eggs safe to drink?

In almost every household case, yes. Greene County Public Health puts it plainly in its water FAQ: "This odor is a nuisance or aesthetic problem and is not harmful to health." There is no federal drinking water standard for hydrogen sulfide, and Penn State Extension explains why: the gas makes water "aesthetically undrinkable long before it reaches harmful concentrations." The Minnesota Department of Health says the sulfur bacteria themselves are not harmful either.

Three caveats worth knowing.

**It is corrosive once there is enough of it.** Ohio State puts that at around 1.0 ppm, where hydrogen sulfide can attack iron, steel, copper and brass, tarnish silverware, and leave yellow or black staining on fixtures. Below that you are mostly dealing with a smell.

**In a confined space it is a genuine hazard.** Hydrogen sulfide is harmless in your glass largely because it leaves the water. Ohio State lists eye, nose and throat irritation, headaches, nausea, fatigue and shortness of breath from breathing it, and loss of consciousness at air concentrations above 500 ppm. That matters in a well pit or a closed pump house. It does not matter at your kitchen sink.

**Sulfate is its own line item.** EPA's secondary standard for sulfate is 250 mg/L, and that number is based on taste, not health. The health number is separate. EPA has a drinking water advisory of 500 mg/L to prevent loose stool and diarrhea in people who are not used to high sulfate, with infants listed as a sensitive group.

So it is not a health emergency. It is a plumbing problem and a quality of life problem.

How do I tell if it is the water, the water heater, or the drain?

Run these checks in order. They take ten minutes and cost nothing.

**Check the drain first.** Fill a glass at the sink that smells, carry it to another room, and smell it there. If the glass is fine away from the sink, your water is fine and the odor is bacteria in the P-trap. Clean the drain. No water treatment will fix that.

**Check hot against cold.** After the house has sat a few hours, smell the hot tap and the cold tap separately. The Minnesota Department of Health flowchart is clear on this one: if the cold water does not smell, the problem is likely in the water heater.

**Check whether it fades.** If both hot and cold smell but the odor drops off after the tap has run a few minutes, that points to sulfur bacteria in the well or the plumbing. If it does not fade at all, the gas is dissolved in the groundwater itself.

**Check a faucet your softener does not feed.** If the smell only shows up downstream of the softener, sulfur bacteria have set up inside it.

Look for physical evidence too. Sulfur bacteria leave a slime that can be white, gray, black, or reddish brown when iron bacteria are in there with them.

Why is sulfur smell common in wells around southwest Ohio?

Two things have to line up. There has to be sulfate in the water, and the water has to be low enough in oxygen that bacteria go after it.

**The sulfate is here.** Ohio EPA's February 2014 fact sheet on Ohio's major aquifers puts typical sulfate in the state's carbonate bedrock aquifers at 90 to 320 ppm, against that 250 ppm secondary standard, largely from gypsum in the rock.

**The oxygen goes away with depth.** Ohio EPA's November 2014 technical report on redox control in Ohio groundwater lays out the order in which groundwater works through its electron acceptors: oxygen first, then nitrate, then manganese, then iron, then sulfate. Rain and snowmelt carry dissolved oxygen down to the water table, and as that water flows down through the aquifer "it is no longer in contact with the atmosphere," so the oxygen gets consumed and the water turns reducing. Deep enough into that sequence and sulfate is what is left to work on. The same report names hydrogen sulfide gas, "with its characteristic rotten egg smell," as one of the by-products.

**Rock type stacks on top of that.** Penn State Extension notes hydrogen sulfide problems are most common in wells drilled into shale and sandstone. Ohio State adds coal and peat deposits. And Ohio EPA's aquifer fact sheet notes that as the share of shale inside the carbonate bedrock rises across southwest Ohio, yields drop, with yields generally under 5 gpm where shale dominates.

One honest qualifier, because this cuts both ways. Plenty of wells around here are not in bedrock at all. The lower Great Miami River buried valley aquifer system, the sand and gravel that USGS studied in the Hamilton area, is one of the most productive aquifers in the region, and Ohio EPA's own table puts typical sulfate in sand and gravel aquifers at 50 to 90 ppm, comfortably under the standard. If your well draws from the buried valley, sulfur odor is less likely to be the aquifer and more likely to be your heater or your bacteria.

Either way it is a normal problem, not a rare one. Greene County Public Health, northeast of us, calls hydrogen sulfide "a natural occurrence in groundwater" that is "quite common in Greene County."

If only the hot water smells, replace the anode rod

Your water heater has a magnesium anode rod in it to keep the tank from rusting. Magnesium reduces sulfate in the water to hydrogen sulfide. Swap the magnesium rod for an aluminum one and the reaction stops. Penn State Extension is direct about it: "Replacement of the magnesium rod with an aluminum rod should eliminate the rotten egg odor while maintaining corrosion protection for the heater."

Do not just pull the rod and leave it out. It does kill the smell, and you will find sources that suggest it, but the rod is the only thing standing between the tank and rust. Penn State says removal "could cause increased corrosion and reduced life of the hot water heater and will likely void the manufacturer's warranty." While the tank is open, flush it.

Be straight about the cost. The rod itself is about forty dollars. Having a plumber install it is not forty dollars. A straightforward swap generally runs somewhere in the $200 to $400 range once you add labor, and more than that if the old rod is seized or there is no clearance above the tank to pull a full length rod. It is still the cheapest fix in this article by a wide margin.

If the smell comes and goes, shock chlorinate the well

Odor that fades once the water has run for a bit is a bacteria problem, and shock chlorination is the standard first move.

The Ohio Department of Health publishes a well disinfection fact sheet with a table for working out your casing water volume and the bleach dose that goes with it. OSU Extension covers the full procedure in fact sheet AEX-318, "Shock Chlorination of Wells."

Two rules from those documents. Use plain unscented laundry bleach, because AEX-318 tells you not to use fresh scent bleach or bleach with detergent. And do not substitute pool chlorine, because ODH warns against solid chlorine products made for swimming pools since they may contain additional chemicals such as algaecides.

Do not skip the casing step either. AEX-318 has you run a hose back down the well to wash down the sides of the casing. That step matters, because the bacteria are living in slime on the casing wall, not floating in the water.

Be realistic about the result. The Minnesota Department of Health notes that sulfur bacteria can be difficult to remove once established in a well. Repeat treatments are common. If it keeps returning, you need continuous treatment rather than another round of bleach.

What actually removes hydrogen sulfide from well water

First, get a number. Hydrogen sulfide vaporizes straight out of a water sample, so Nebraska Extension says the sample has to be stabilized or the test has to be run at the source. Virginia Tech says the same thing: samples "must be stabilized immediately," and most labs will hand you a bottle with the preservative already in it. Water you carry to a lab in a jar will read low.

Then match the equipment to the number. These first three ranges are Virginia Tech Extension's:

- **A few tenths of a mg/L.** Activated carbon filtration. Simple, and the media has to be replaced on a schedule. - **Up to 6 mg/L.** An oxidizing, iron removal filter containing manganese greensand, which converts the gas to solid sulfur particles and filters them out. It needs backwashing and periodic regeneration. - **Above 6 mg/L.** Injection of chlorine or potassium permanganate into the plumbing, followed by filtration to catch the sulfur. - **Aeration** is the option that adds no chemicals. Penn State and Ohio State both cap it at about 2 mg/L.

A water softener is not a hydrogen sulfide treatment. It is an excellent hardness treatment and a bad odor treatment. It can even become part of the problem: Penn State notes that a softener can give sulfur-reducing bacteria a favorable place to grow.

What if I am on city water in Cincinnati?

If you are on Greater Cincinnati Water Works, the smell is almost certainly your drain or your water heater, not the water arriving at the house.

GCWW disinfects with free chlorine, which is an oxidizer. Hydrogen sulfide does not survive contact with it, so it is not coming through the main. Your anode rod, on the other hand, does not care where the water came from. Magnesium reacting with sulfate in city water makes the same gas it makes on well water. So run the same two checks: the glass test for the drain, and hot against cold for the heater.

Hardness is the separate, real issue on city water here. Using the Water Quality Association's bands, 7 to 10.5 grains per gallon is hard and anything above 10.5 is very hard. GCWW runs 7.4 grains per gallon out of the Richard Miller plant on the Ohio River and 8.2 out of the Bolton plant on the Great Miami aquifer. Both sit in the hard band.

Xenia runs 23 gpg and Oxford 20 to 22 gpg, both very hard. Indian Hill at 8.8 to 9.9 and Harrison at about 8 sit in the same hard band as GCWW, though Harrison used to run 21 gpg before its reverse osmosis softening plant came fully online on 3 October 2022.

That is a softener conversation, not a sulfur conversation. Keep the two apart.

Getting it fixed

Sort out the cause first, because the three causes do not lead to the same place.

**If it traces to the anode rod,** call a plumber and swap the rod. We will tell you that on the phone, and there is nothing for us to sell you.

**If it traces to bacteria,** shock the well and see how long it holds.

**If you have real dissolved hydrogen sulfide in the groundwater,** that needs equipment built for hydrogen sulfide and sized to a test result: an oxidizing filter, aeration, or chemical injection, depending on the number. Our Complete Home System is not that. It is a softener and reverse osmosis package, and as this article says, a softener does not remove hydrogen sulfide. Call us with your test result and we will tell you what it actually calls for, including when that is a plumber and not us.

Where the Complete Home System does fit is hardness, which on Cincinnati water is the problem nearly everybody actually has. It is $3,492 installed, flat rate, with a lifetime tank warranty and a five year valve warranty. Installation is free on garage, basement and utility closet installs. The annual reverse osmosis filter change is $199.

Call us at (513) 466-0716 and we will help you work out which of the three causes you have before anyone quotes you equipment.