Rotten-Egg Smell From a Well: The Hot-Tap Test That Tells You Whose Job It Is

Run the cold tap by itself for a minute, then run the hot tap by itself. If the rotten-egg smell only turns up on the hot side, the source is almost certainly the magnesium anode rod inside your water heater reacting with sulfate in the water — a plumbing repair, and one that is squarely ours. If it is on both sides, hydrogen sulfide is arriving from the well itself, which is a well and water-treatment problem rather than a plumbing one. Same smell, two entirely different phone calls.

What the smell actually is

Hydrogen sulfide, in almost every case. It forms in groundwater as a by-product of sulfur-reducing bacteria, which live comfortably in the low-oxygen conditions inside a well and inside plumbing. Your nose is an extraordinarily good detector for it: Penn State Extension puts the threshold at levels well below 0.5 milligrams per litre, which is far under any concentration that would show up as a taste or a stain.

This is not a national-average problem imported into a local article. The U.S. Geological Survey wrote it down for this county specifically. In Ground-Water Resources Data for Baldwin County, Alabama (Open-File Report 96-487, Robinson, Moreland and Clark, 1996, prepared with the Baldwin County Commission), the abstract reads: "The quality of ground water generally is good, but problems with iron, sulfur, turbidity, and color occur." The same report's ground-water quality section is more specific still — in coastal areas hydrogen sulfide and methane may occur, and ground water with a dissolved-solids content exceeding 1,000 mg/L, a chloride content of 500 mg/L and a sulfurous odour occurs in the areas adjacent to the Mobile River and locally near the Gulf of Mexico.

Then the line that matters most to anyone reading this on a well: "The water from most private wells in Baldwin County is used without treatment or filtration."

That is the whole difference between a well address and a utility address. A registered public system in this county gets a treatment step in the middle — USGS records that beyond the chlorination Alabama public-health law requires, the most common treatment by Baldwin County public suppliers is pH adjustment, iron removal and aeration. A private well has no middle. Whatever the aquifer hands over is what reaches your fittings.

Streamlined Plumbing covers Stockton and the Tensaw River corridor at the northern end of the county, and Stockton is one of only 10 of the 22 communities Streamlined Plumbing serves with no registered municipal community water system (private wells). Look at a map of the delta and USGS's phrase "adjacent to the Mobile River" stops being abstract: the rural Stockton timber land and the addresses off Hwy 59 north of Bay Minette sit along the eastern edge of the ground that sentence is pointing at. That is a reason to test rather than a diagnosis of any particular well.

Is it the well or the water heater?

Do the test properly, because a sloppy version of it produces a wrong answer.

Run the cold tap at a fixture that is nowhere near the water heater — an outside hose bib is ideal — for a full minute, then smell it. Then run the hot tap at that same fixture, or the nearest one, for a full minute and smell that. Do not mix them at a single-handle faucet, and do not judge it off the first ten seconds, which will just be whatever sat in the branch line overnight.

Cold clean, hot smelly: the water heater. Both smelly: the well. Both clean, but the shower smells: you are probably chasing a drain, not water.

The magnesium rod is doing more work here than almost anywhere

Every steel storage tank has an anode rod threaded into it — a bar of sacrificial metal that corrodes so the tank's steel lining doesn't. Magnesium is the usual material because it is the most electrically active of the options and therefore the most protective.

It is also the one that causes this smell. Magnesium can chemically reduce sulfate in the water to hydrogen sulfide, which is why the gas appears inside the tank and travels out on the hot side only.

The fix is a material swap, not a deletion. An aluminum or zinc-alloy rod keeps the tank protected while ending the reaction that produces the odour. Pulling the rod and leaving the hole plugged stops the smell and starts a countdown on the tank instead, and it will generally void the manufacturer's warranty. If the tank is already old enough that its rod has never been inspected, the honest conversation is about repair versus replacement rather than about the rod alone, and on a well property in Bon Secour or out at Fort Morgan the drive is long enough that it is worth having that conversation on the phone before anybody sets out.

If the house runs a tankless unit instead, there is no anode rod and no storage volume, so hot-side-only odour is not the likely story — that one points back at the well.

If it is in the cold water too, this is the well side

At that point the gas is coming out of the ground, and none of the remedies are plumbing repairs.

The recognised options are all treatment or well work: shock chlorination of the well, which usually knocks the bacteria back temporarily rather than permanently; aeration for low concentrations; oxidising filters using manganese greensand in the low single digits of mg/L; activated carbon below about 1.0 mg/L; continuous chlorination with filtration above roughly 6.0 mg/L. Choosing between those requires a measured concentration, which means a test before equipment.

Here is where the line sits, stated plainly. We do not drill, service, pull or repair wells or well pumps, we do not service pressure tanks, and we do not sell or install water treatment. Alabama licenses water well drillers through the Alabama Department of Environmental Management's Water Well Standards Program, and ADEM Admin. Code r. 335-9-1 requires a licensed driller to file a Notification of Intent before work and a Certification of Completion within 30 days after it. A licensed well contractor and a water-treatment company are the two calls for anything on that side of the pressure tank. We would rather name them than pretend the whole problem is ours.

The smell people mistake for this one

Sewer gas. It is also sulfurous, and it also turns up in houses that sit empty — which describes a lot of camps and seasonal places, from the water out to rural Perdido acreage along the Perdido River corridor.

The difference is where it lives. A dry P-trap or a compromised vent stack lets sewer gas into one room, with the water off, near one fixture. Well-borne hydrogen sulfide rides in the water and appears anywhere that water runs, including in a glass. If the smell is confined to a bathroom nobody has used since summer, pour a couple of litres of water down every drain in it and see whether it goes away — that is a drain and vent question, not a water question, and it is one we handle.

What we can actually do about it

On the plumbing side, the honest list is short and real: inspect and replace the anode rod, flush and service the heater, replace a tank that is past arguing with, replace fixtures and cartridges that sulfide has blackened or fouled, and clear a drain line that has gone slimy. Those are repairs, and they are ours.

On the water side, the useful thing we can do is tell you what test to get and how to read it before you spend money on equipment. The route for a Baldwin County well runs through the county health department for bacteriological work and an EPA-certified lab for everything else — that is laid out in how to get a private well tested in Baldwin County. And if the well and the plumbing have never had their boundary drawn for you, where the well ends and the plumbing begins is the map.

We answer around the clock at (251) 423-7654. Brandon Byrd, Alabama Master Plumber MP-4462.

Sources. USGS Open-File Report 96-487, Ground-Water Resources Data for Baldwin County, Alabama (Robinson, Moreland and Clark, 1996), abstract and Ground-Water Quality section. USGS Water Quality Portal, Baldwin County well samples for hardness (177 results, median 12 mg/L CaCO₃, 87% under 60 mg/L), retrieved 2026-08-01. Penn State Extension, "Hydrogen Sulfide (Rotten Egg Odor) in Water Wells." EPA, National Secondary Drinking Water Standards. ADEM Admin. Code r. 335-9-1, Water Well Standards Program.