Disclaimer: This content is for general information only. Water heater and well system work can involve chemical, electrical, and pressure hazards. When in doubt, consult a licensed professional.
You might have experienced turning on your hot water only to face a nauseating rotten egg smell. This unpleasant odor in your hot water comes from hydrogen sulfide gas, a sulfur-based byproduct that bacteria create in your water heater.
The rotten egg smell from your hot water heater signals more than just an annoyance. A chemical reaction inside your water heater creates this smell as sulfate bacteria grow within the tank. The degrading anode rod inside your hot water tank makes this rotten egg smell even worse. People exposed to this hydrogen sulfide gas at low concentrations might experience burning eyes, headaches, nausea, and dizziness.
The good news is you don’t need to tolerate this offensive odor. Simple fixes can address the causes that make hot water smell like rotten eggs. Your water heater creates an ideal environment that converts sulfate to hydrogen sulfide gas. This piece will help you identify the smell’s source and implement solutions that will make your water smell fresh again.
What causes hot water to smell like rotten eggs?
That rotten egg smell from your hot water taps isn’t just gross—it’s hydrogen sulfide gas that forms through specific chemical and biological processes. Let me walk you through the four biggest problems that cause this awful smell.
Bacteria buildup in the water heater
The sulfur smell usually comes from sulfate-reducing bacteria that exist naturally in many water supplies. These pesky but harmless microorganisms love the warm, oxygen-free environment inside your water heater tank. These bacteria feed on tiny amounts of sulfur compounds in the water and produce hydrogen sulfide gas.
Your water heater’s low temperature creates perfect conditions for these bacteria. They can hide in small cracks in your water heater’s tank lining and multiply faster. The bacteria won’t hurt you, but they create that unmistakable rotten egg smell that makes hot water unbearable.
Reaction with magnesium anode rod
The sacrificial anode rod in your water heater is the most likely culprit behind smelly hot water. Most water heaters have a metal rod called an anode, usually made of magnesium, that protects the tank from corrosion.
This rod attracts corrosive elements away from the tank walls—basically taking the hit to protect your water heater. The magnesium anode rod reacts with sulfates that naturally occur in your water supply and creates hydrogen sulfide gas. This chemical reaction leads to that classic rotten egg smell, especially in well water systems.
You might find it strange that a new water heater starts to smell while your old one never did. This happens because manufacturers now use more magnesium anodes in newer water heaters.
Contaminated well water
Well water systems often have problems with hydrogen sulfide. This gas shows up naturally in groundwater because of sulfur-reducing bacteria. These tiny organisms eat small amounts of sulfur in the water and thrive in well water’s low-oxygen environment.
Some areas have so much sulfur that both hot and cold water smell bad. Water softeners can make things worse. They sometimes create the perfect environment for sulfur-reducing bacteria.
Stagnant water in unused tanks
Bacteria love to grow in water that sits still. A hot water tank that hasn’t been used creates the perfect breeding ground for them. These organisms multiply faster in calm, warm water that hasn’t moved for several hours.
This problem shows up a lot in vacation homes, guest bathrooms, or backup water heaters. Bacteria multiply in unused water and produce more hydrogen sulfide gas. The smell hits you hard when you first turn on the tap after a long break, but it usually gets better as fresh water runs through.
These causes are the foundations of fixing that nasty sulfur smell in your hot water system.
How to tell where the smell is coming from
You need to find the exact source of your smelly water problem before fixing it. The unpleasant rotten egg odor can be tracked down with some simple detective work at home, before you need a professional. Here’s a step-by-step way to find what’s causing the smell.
Test hot vs cold water
The first step is to check if the problem affects your hot water, cold water, or both. Run both hot and cold water taps separately after being away from home for a few hours. Notice which ones give off that distinctive sulfur smell. The problem likely comes from your water heater if only the hot water smells like rotten eggs and cold water stays fresh. The issue could be in your groundwater supply or plumbing system if both hot and cold water smell bad.
Temperature makes a difference because hot water releases hydrogen sulfide gas more quickly than cold water. So even small amounts of contamination (as little as 0.5 mg/l) can create noticeable odors in hot water systems.
Check if smell is in all faucets
The next step is to test every faucet in your home. The main water supply is likely the source if the smell shows up at all water faucets. The problem probably lies in the fixtures or pipes that serve specific locations if the odor only appears at certain faucets.
A simple “glass test” can help. Fill a clean glass with water from the affected faucet and walk to another room. Smell the water after swirling it in the glass—the problem is in your water supply if the odor stays in the glass, not the drain. The issue likely exists within your household plumbing system rather than your main water source if the smell fades after running water for several minutes.
Inspect water softener and plumbing
Sulfur and iron bacteria often grow inside water softeners and create rotten egg odors. Disconnect your faucet from the water softener system to see if it’s causing the problem. You’ve found the source if the odor goes away after bypassing the softener—your water softener probably contains sulfur bacteria and needs a good cleaning.
Homes with well water systems should also test faucets not connected to the water softener. Compare softened and non-softened water to find whether the problem starts in the softener or somewhere else in your system.
Look for black stains or slime
The rotten egg smell often comes with visible signs. Look for black or gray stains on fixtures, silverware, or inside pipes. These marks usually mean hydrogen sulfide gas is present in your water.
Bacterial slime is another thing to watch for. It can be white, gray, black, or reddish-brown (especially with iron bacteria). This slime forms when sulfur bacteria colonies grow in your plumbing system. Watch for corroded pipes and metal parts in your water system too, since hydrogen sulfide gas can seriously damage plumbing.
These diagnostic steps will help you pinpoint where your rotten egg smell starts—vital information to fix your specific problem.
Simple fixes for rotten egg smell in hot water
You’ve found the source of that rotten egg smell. Now let’s get rid of it. Here are five budget-friendly ways to make your hot water fresh again. The best part? You don’t need to be a plumbing expert.
Flush the water heater tank
Your water heater needs a good flush to remove sediment and bacteria that make it smell bad. This basic maintenance task should happen at least once a year:
- Turn off the power or gas supply to your water heater
- Shut off the cold water inlet valve
- Connect a garden hose to the drain valve at the bottom of the tank
- Open the valve and drain the tank completely
- Close the drain valve, refill the tank, and restore power
A good flush doesn’t just kill the smell – it helps your water heater run better and last longer.
Replace the anode rod with zinc or aluminum
The magnesium anode rod in your water heater can react with bacteria and create that sulfur smell. A zinc or aluminum-zinc alloy rod works better:
- Turn off power to the water heater
- Drain some water from the tank to lower the water level
- Locate and remove the old anode rod using a socket wrench
- Install the new aluminum-zinc rod
- Refill the tank and restore power
Aluminum-zinc alloy rods work better because they don’t interact with bacteria like magnesium rods do. This cuts down hydrogen sulfide production by a lot.
Disinfect the tank with chlorine
Tough smells need stronger treatment. Chlorine bleach or hydrogen peroxide can kill those smelly bacteria quickly:
- Turn off the water heater and close the cold water supply valve
- Drain some water from the tank
- Add one gallon of household bleach for every 25 gallons of tank capacity
- Refill the tank and run hot water through all faucets until you smell chlorine
- Let sit overnight, then flush the system thoroughly
Hydrogen peroxide makes a safer choice than chlorine bleach while working just as well.
Raise water temperature temporarily
A temperature boost to 140°F (60°C) for several hours kills odor-causing bacteria. Just make sure to lower it back to 120°F afterward to prevent scalding.
Your water heater needs a working pressure relief valve before you try this method.
Install a water purification system
Stubborn sulfur smells that keep coming back might need a whole-house water treatment system:
- Sulfur filtration systems remove hydrogen sulfide gas before it enters your home
- These systems use oxidation processes or specialized media to treat contaminated water
- They eliminate odors from all fixtures and protect your pipes from corrosion
Need help with any of these fixes? A licensed plumber who knows water quality can help you out.
When the problem is in your well or plumbing system
Your rotten egg smell might not be coming from your water heater at all. The real culprit could be your well or plumbing system. Sulfur-reducing bacteria in these areas create hydrogen sulfide gas that makes your entire water supply smell awful.
Disinfect the well and plumbing
Shock chlorination works best to eliminate bacterial contamination in well systems. You’ll need to pour a strong chlorine solution straight into the well to kill those sulfur bacteria. The right mix is about 3 pints of regular household bleach for every 100 gallons of water. These bacteria can be tough to remove once they’ve made themselves at home in a well. You might need to scrub the well casing and use special treatment chemicals before the process works properly.
Use oxidizing filters or chlorination
Stubborn hydrogen sulfide problems need specialized treatment systems. Oxidizing media filtration systems can handle hydrogen sulfide levels up to 6 mg/L effectively. Air injection oxidizing filters give you an eco-friendly option. They use catalytic carbon or iron-removal media to trap odor-causing elements. Another reliable fix combines continuous chlorination with carbon filtration to permanently remove sulfur smells.
Consider drilling a new well
Municipal water connection or a new well might be your best bet sometimes. A shallower well could give you sulfur-free water by staying above deeper sulfur-bearing rock formations. The upfront cost seems high, but it could save you money compared to buying and maintaining water treatment equipment long-term.
Contact a licensed well contractor
Complex sulfur problems need professional help. Licensed well contractors can give you a full picture with downhole camera assessments to spot structural issues. These experts know which solutions will work best, from fixing up your existing well to installing specialized filtration. They have the know-how to handle tough pre-treatment work that badly contaminated wells need.
Does your well water smell like rotten eggs? Transit & Flow’s expert plumbing service in Columbus, Ohio can help. Call (614) 333-8092 today.
How to prevent the smell from coming back
You can stop that nasty rotten egg smell from coming back through regular maintenance and good decisions. A few simple steps will help you avoid this issue in the future.
Turn off heater if away for long periods
Don’t let water sit in your water heater when you’re gone for a while. You should turn off the gas to your water heater if you’ll be away for more than two weeks. While cold water can stay in the tank without bacteria growth, you might want to drain the tank completely for longer absences.
Flush the tank regularly
You need to flush your tank yearly to get rid of sediment and bacteria buildup. The U.S. Department of Energy says this yearly maintenance helps prevent odors, makes your system more efficient, and helps your water heater last longer.
Use a different anode rod material
You should switch from standard magnesium anode rods to other materials. Zinc-infused aluminum rods help neutralize the bacterial reaction that creates hydrogen sulfide gas. Powered titanium anodes offer a lasting solution that breaks down sulfate ions and stops bacteria from multiplying.
Install whole-house water treatment
A complete filtration system keeps contaminants away from your water heater. Your chances of bacterial growth and smelly chemical reactions drop significantly with whole-house filtration. This solution works great especially when you have well water or known water quality issues.
Contact Transit & Flow at (614) 333-8092 for expert assistance with water heater maintenance and water quality solutions in Columbus, Ohio.
Conclusion
That nauseating rotten egg smell from your hot water doesn’t have to stick around forever. We’ve found that hydrogen sulfide gas is the biggest problem behind this unpleasant odor. This gas comes from sulfate-reducing bacteria and reactions with magnesium anode rods. The good news is you have several ways to fix this.
Simple solutions work well to start. You can flush your water heater tank once a year or switch your standard magnesium anode rod with a zinc or aluminum one. On top of that, you can kill stubborn bacteria by disinfecting your tank with chlorine or hydrogen peroxide. Whole-house water purification systems are a flexible option for tough problems, especially when you have well water issues.
Taking preventive steps matters just as much as treatment. Keep in mind that turning off your water heater during long trips, doing regular maintenance, and upgrading to better anode rod materials will help keep those rotten egg smells away for good.
You can handle some fixes on your own, but complex problems might need expert help. This is especially true with well water systems or when you need specialized equipment. Professional plumbers can pinpoint the exact cause and implement the right solution for your situation.
Don’t let bad smells affect your home life. Transit & Flow’s team will help bring back your water’s freshness and stop those rotten egg smells from coming back. Call us at (614) 333-8092 for expert water heater maintenance and water quality solutions in Columbus, Ohio.