Well Water Smells Like Rotten Eggs: A New Jersey Diagnostic Guide

Before you test any faucet, separate two things that smell alike. Utilities add an odorant to natural gas so leaks can be found by nose. PSE&G describes it this way: "An odorant called Mercaptan is added to natural gas before use, so that gas leaks can more easily be detected." The same page cautions that you should not rely only on your sense of smell, because the odorant can be weak or hard to detect even when there is a leak.

PSE&G lists other warning signs of an outdoor gas leak: a hissing, roaring, whistling or blowing sound from the ground or a gas appliance, dust or debris blowing from a hole in the ground, a white cloud, mist or fog, water bubbling in standing water or around a valve box, and a ring of dead grass in an otherwise green area.

If you smell rotten eggs in the air rather than in running water, PSE&G says to exit the building immediately, move at least 350 feet away, and from that safe distance call 1-800-880-7734 or 911. Its list of things not to do includes using light switches or doorbells, using a telephone or cell phone, starting a car, smoking or vaping, turning appliances or flashlights on or off, and trying to find the source of the odor yourself.

There is a second air risk that is specific to wells. The Minnesota Department of Health warns that hydrogen sulfide gas in air can be harmful at high levels and can collect in low-lying spaces such as well pits and basements, or enclosed spaces such as well houses, and that only well professionals using proper safety precautions should consider entering them. If the odor is strongest in a basement or pit rather than at the tap, treat that as a job for a professional.

If the smell only shows up when water is running, it is a water problem. Keep going.

Run this test after you have been away from the house for a few hours, so water has been sitting in the pipes and in the heater. At one sink, smell the cold tap and the hot tap separately. The Minnesota Department of Health publishes the flowchart below in its well water brochure, and the logic works the same on a New Jersey well.

One more check is worth thirty seconds. If the odor seems to come from a single bathroom, fill a glass at that sink, carry it to another room and smell it there. If the glass has no odor, the smell is coming from the drain or the trap, not the well, and no filter will fix it.

Write down what you find before you call anyone. The answers to those three questions decide whether you need a plumber, a well contractor, a disinfection, or treatment equipment.

If the cold tap is clean and only the hot side smells, the reaction is happening inside your tank. Most water heaters contain a metal rod called an anode, installed to reduce corrosion of the tank. Minnesota's well program explains that the anode is usually magnesium, "which can supply electrons that aid in the conversion of sulfate to hydrogen sulfide gas." The rod is 1/2 to 3/4 inches in diameter and 30 to 40 inches long. A warm tank also makes a comfortable home for sulfur bacteria.

Minnesota's own advice on this branch is blunt: unless you are very familiar with water heater operation and maintenance, have a plumber or water system professional do the work. Three published options exist.

• Change the anode material. Penn State Extension notes that replacing the magnesium rod with an aluminum rod "should eliminate the rotten egg odor while maintaining corrosion protection for the heater." Minnesota warns that pulling the anode and simply plugging the hole "may significantly decrease the life of the water heater," so removal without replacement is a poor trade.
• Disinfect and flush the tank with a chlorine bleach solution. Minnesota notes that chlorination can kill sulfur bacteria, but if all bacteria are not destroyed, the problem may return within a few weeks.
• Raise the tank temperature to 160 degrees Fahrenheit (71 degrees Celsius) for several hours, then flush out the dead bacteria. Minnesota attaches a clear caution to this one. Increasing the temperature can be dangerous, the manufacturer or dealer should be consulted about an operable pressure relief valve, and the thermostat has to be lowered afterward to prevent injury from scalding hot water and to avoid high energy costs.

Because this touches a pressure vessel and a potable water line, we have this work done by licensed New Jersey master plumbers, and so should anyone else.

A rotten egg smell that shows up on both hot and cold taps and then gets weaker after a few minutes of running usually means bacteria are living in the standing water inside the well or the pipes, not in the aquifer feeding them. Minnesota states that sulfur bacteria are not harmful, but they produce a slime that can clog wells, plumbing and irrigation systems, and the slime "can help other bacteria grow, such as iron bacteria."

The published fix is disinfection, not filtration. Minnesota's guidance is to disinfect the well and plumbing system with a strong chlorine solution, and it adds an honest warning: "Sulfur bacteria can be difficult to remove once established in a well." Prework such as scrubbing the well casing, using special treatment chemicals and agitating the water before disinfection may be necessary, especially if iron bacteria are also present, and Minnesota says to contact a licensed well contractor to do that prework.

Iron bacteria give themselves away. Minnesota describes sticky rusty, yellow, brown or grey slime, feathery or filamentous growths in standing water, a rainbow colored oil-like sheen, and odors people call "swampy, oily or petroleum, cucumber, sewage, rotten vegetation, or musty." For iron bacteria the state describes shock chlorination at a concentration close to but not greater than 200 parts per million, and pasteurization that holds the well water at 140 degrees Fahrenheit for 30 minutes, which it calls effective but expensive.

If the smell disappears at faucets that bypass the softener, the bacteria are in the softener or another treatment device. Minnesota says to contact the installer or manufacturer for disinfection instructions rather than guessing at a bleach dose.

When the odor holds steady no matter how long the water runs, the gas is dissolved in the aquifer. USGS explains that this happens "when water comes into contact with organic matter or with certain minerals, such as pyrite," mostly as groundwater filters through organic material or rocks. Penn State adds that hydrogen sulfide problems are most common in wells drilled into acidic bedrock such as shale and sandstone. Water chemistry matters here too: the World Health Organization notes that hydrogen sulfide concentrations increase as pH decreases.

Your nose is more sensitive than most regulations. WHO estimates the taste and odour thresholds for hydrogen sulfide in water at 0.05 to 0.1 mg/litre, and Penn State says most people can detect levels well below 0.5 mg/L. WHO reviewed the oral toxicity data and concluded that "no health-based guideline value is proposed," while still saying hydrogen sulfide "should not be detectable in drinking-water by taste or odour." In plain terms, you will smell it long before any number turns into a health limit, which is exactly why this is treated as an aesthetic problem.

Published treatment ranges differ by source, which is the strongest argument for getting a lab number before buying anything.

University of Georgia Extension adds a limit that catalog shopping tends to hide: oxidizing filter media "should not be used on water supplies with hydrogen sulfide over 5 ppm, iron exceeding 10 ppm, or combined iron and manganese exceeding 15 ppm." UGA also notes that hydrogen sulfide consumes the manganese oxide coating on the filter medium faster than iron does, exhausting the media's capacity more quickly.

Air injection oxidation systems, often sold as AIO, are a packaged version of aeration plus filtration in a single tank, and manufacturers market them for iron, manganese and sulfur together. They can be a good fit, but sizing depends on your actual iron, sulfide, pH and flow numbers, so treat any recommendation made without a lab report as a guess.

Choosing an iron filter for well water starts with what form the iron is in, not with brand names. Penn State describes two states: water that is "initially clear but then forms orange-brown or black solid particles over time," which is dissolved ferrous iron, and water where solid particles are present immediately, which is oxidized ferric iron. A third form, iron bacteria, is alive and does not respond to filtration at all.

Two cautions come straight from the extension literature and are worth repeating, because they are where money gets wasted. First, oxidized iron fouls softener resin. Penn State says it is critical that raw water not come in contact with oxidizing agents like air or chlorine before entering the softener, and discourages using the resin bed as a mechanical filter for oxidized metals because it can damage the resin and force frequent backwashing. Softeners sold for iron duty should be certified to NSF/ANSI 44 for cation exchange water softeners.

Second, polyphosphate feed, which is sometimes offered as a cheap fix below 2 mg/L of dissolved iron, does not remove iron. It sequesters it. Penn State notes the water keeps a metallic taste, too much phosphate makes water feel slippery, and the polyphosphate can break down in the water heater and release the iron anyway.

Media choice also has chemistry limits. UGA's media table lists manganese greensand as operating between pH 6.2 and 8.8, and Birm as needing pH 6.8 or higher plus dissolved oxygen equal to at least 15 percent of the iron concentration, so 10 ppm of iron calls for at least 1.5 ppm of dissolved oxygen. On a low pH New Jersey bedrock well, that difference decides whether a filter works or sits there doing nothing.

Staining is free evidence, and it points at different metals. EPA's secondary drinking water standards are non-enforceable guidelines for taste, color and odor rather than health limits, but they are the numbers labs compare your results against.

New Jersey bedrock gives this some local shape. A 2004 New Jersey Geological Survey report by Michael Serfes sampled 105 wells in the Highlands and Valley and Ridge provinces, across Bergen, Essex, Hunterdon, Morris, Passaic, Sussex and Warren County. About 45 of those wells were in the Middle Proterozoic crystalline rock that forms the Highlands ridges. In that group, manganese exceeded 0.05 mg/L in 16.3 percent of samples and iron exceeded 0.3 mg/L in 6.7 percent, about 30 percent came in below pH 6.5, and 84 percent fell below minus 1 on the Langelier index, which the report calls very corrosive. Sulfate was low, with a maximum of 42 mg/L against a 250 mg/L standard. The same report found gross alpha particle activity above the 15 picocuries per liter primary standard in 4 of 21 crystalline aquifer samples.

Read that as background, not as a prediction. It is one survey, it is more than twenty years old, and bedrock wells vary sharply from one property to the next. What it does suggest is that in this part of the state, low pH and manganese deserve as much attention as iron, and that blue-green staining on a Morris County well is worth taking seriously rather than scrubbing off.

Jersey Water Pros does not test water. We help homeowners arrange testing through an NJDEP-certified laboratory, and NJDEP publishes a certified laboratory list through its Division of Science and Research. That is the only result worth designing a system around.

Check your closing file first. New Jersey's Private Well Testing Act requires well water testing in connection with the sale or lease of a home served by a private well. Certified laboratories that run the panel list iron, manganese and pH among the required parameters, along with coliform bacteria, nitrate, lead, arsenic and gross alpha, so if you bought your home since the law took effect you may already own a usable baseline without paying for anything new. One certified lab's published parameter list also notes that uranium testing is required for wells in Essex, Morris and Union County, among others, which covers all three of the counties we serve. Confirm the current requirements with NJDEP or your lab, since the panel has changed over the years.

Two testing details matter for this particular problem:

• Hydrogen sulfide will not survive the drive to the lab. Penn State notes that testing must be done in the home, or the sample must be chemically stabilized before being sent to a commercial testing lab, because the gas escapes. Ask the lab for its sulfide procedure before you collect anything.
• Add coliform bacteria and nitrate when the smell is new. Minnesota's guidance is that in most cases the rotten egg smell does not relate to the sanitary quality of the water, but in rare instances the gas may be from sewage or other pollution, so it recommends testing for those two.

On cost, published ranges vary widely and none of them are a New Jersey quote. One out of state online water treatment retailer's price guide, updated in February 2026, publishes roughly $800 to $1,200 for budget online systems, $1,800 to $2,500 for its own wholesale tier, and $5,000 to $10,000 for high-end local franchise pricing. Read that with the obvious caveat that the seller is quoting its own tier against its competitors. Real numbers depend on your iron, manganese, sulfide and pH readings, your flow rate, your bathroom count and how the equipment has to be plumbed into an existing basement.

Jersey Water Pros is based in Summit and serves Union, Essex and Morris County. Every installation is performed by licensed New Jersey master plumbers working as our subcontractors. New Jersey licenses master plumbers through the State Board of Examiners of Master Plumbers at the Division of Consumer Affairs, and you can verify any plumber's license there. If you have run the three questions above and know which branch you landed on, bring that answer and any lab results to a free quote at /free-estimate, and we will size the fix around your numbers rather than around a catalog.