Smelly water from hot water heater, burns eyes when showering (Peggie still here?)

[Captain Larry-DH]

After more than 50 years of boating, mostly in the northeast where we winterize boats - this is a new one for me. My boat has 2 water heaters, one for each side (catamaran). When winterizing, I bypass and drain the water heaters and use potable antifreeze in the remainder of the lines. In Spring, I run out the antifreeze, shock the system with chlorine bleach solution, then clear out the bleach and reconnect the water heaters.
No problems until yesterday, when I showered in the side of the boat we normally don't use. There was a distinct odor to the water, and it irritated my eyes and mildly stung an open cut on my arm. Maybe it's acidic? I don't think it's residual antifreeze, and it doesn't smell like a type of mold or fungus. I ran out at least 10 gallons of water (it's a 6-gallon heater tank) and it smells much less but it's still barely detectable to me (wife doesn't smell it, so it's not strong).
Any thoughts about this?
Edit - my next step is to bypass the tank again and drain it, then refill with fresh water.

 

[kappykaplan]

Larry, Peggie Hall HeadMistress hasn't been seen since 20 Jan 2026.

 

[Captain Larry-DH]

Larry, Peggie Hall HeadMistress hasn't been seen since 20 Jan 2026.

Hmmm, yeah. Hope she’s ok.

 

[kappykaplan]

Hope she’s ok.

 

[dlochner]

Smelly hot water tanks are often the result of depleted anodes. Pull one of the anodes and take a look. At least on the Raritan tanks the anode is part of the HW outlet.

 

[thinwater]

Smelly hot water tanks are often the result of depleted anodes. Pull one of the anodes and take a look. At least on the Raritan tanks the anode is part of the HW outlet.

^^ Possibly.

The irritating gas is hydrogen sulfide, which is produced from the sulfate present in the tap water.

Another source, if the bleach had been gone for a while, is that sulfide reducing bacteria were in the tank again.

The other solution is to treat your water with bleach on a regular basis (every fill). Homes that constantly flow chlorinated water through the heater don't get this, but by the time the water gets to the end of the hose, and if the water is left in the tank a while, the rules change.

 

[Ralph Johnstone]

There was a distinct odor to the water, and it irritated my eyes and mildly stung an open cut on my arm.

Did it smell anything like rotten eggs ?

 

[Stu Jackson]

Peggie's still around. At least her book is.

But the info is out there, like this one:

Fresh Water System Recommissioning 101 - Peggie Hall's "Cocktail" Rotten Egg Odor http://c34.org/bbs/index.php/topic,5836.0.html

 

[Captain Larry-DH]

Thanks for the responses. No this is not a rotten egg issue. And there was no anode installed, ever. I’m going to bypass and drain the tank. Then figure out a way to shock it with chlorine.
ChatGPT says the following (italics added):

With a stainless steel tank and no anode rod, you can essentially rule out the classic "rotten egg" problem caused by a magnesium anode reacting with sulfate-reducing bacteria.
Given that:

• The odor is only in the hot water.
• It's only one water heater.
• The heater was bypassed during spring chlorination, so it was never disinfected.
• The side is rarely used, allowing water to sit for months.
• Flushing about 10 gallons (more than the heater's capacity) noticeably reduced the odor.

I think the most likely explanation is bacterial or biofilm growth inside the water heater, rather than a chemical problem.
Why the eye irritation?
Some bacteria produce volatile organic compounds (VOCs) that become airborne in a hot shower. Even at low concentrations, these can irritate sensitive tissues like your eyes. If the water also has a high bacterial count, the metabolic byproducts can sometimes sting a fresh cut as well. That doesn't necessarily mean the water is unsafe, but it does indicate the heater should be cleaned.
My recommendation
I'd treat this heater as though it missed its spring commissioning:

1. Drain the heater completely.
2. Refill it with a chlorine solution strong enough to disinfect the tank. A common target is about 50–100 ppm free chlorine. For a 6-gallon heater, that works out to roughly:
   • ½ to 1 fluid ounce (15–30 mL) of regular unscented household bleach (5–8.25% sodium hypochlorite), then fill the rest with fresh water.
3. Let it sit for 2–4 hours (overnight is acceptable if the concentration is on the lower end).
4. Drain it completely.
5. Refill and flush until the chlorine odor is gone.

Because your plumbing was already sanitized in the spring, you don't necessarily need to disinfect the entire freshwater system again unless you notice the odor elsewhere.

 

[sailcapt340]

Where did you last fill your tank with “new” water? I ask because a few years back the same happened to us after refilling our water tank with from another marina. Just after that the town issued a boil water alert. Then came the bacteria from the water source introduced into our tank. We caught it by the foul smell of the water out of the tap.

What I did was drain the system, flush out the entire system (including the water heater).
Bleach solution according to Peggy Halls method. Why eliminate the water heater from the cleansing process, you’re not winterizing, you’re sanitizing. Any bacteria that is hiding in elbows and tees will just join in the new water.
And be certain of the water source you use going forward. That in itself may not be easy but has to be looked at.

 

[Captain Larry-DH]

Why eliminate the water heater from the cleansing process,

The hot water tanks had been sitting empty (except perhaps some small residual) for the winter. Easier to get full evacuation of the chlorine if there aren’t 2x 6-gallon tanks in the system that fill and empty a fraction each time they're used. (How much fresh water does it take to flush 6 gallons of heavily chlorinated water in tank that uses half-inch lines?). That’s why I don’t use antifreeze in them either, along with cost.
Don’t forget, this isn’t an issue for the other one. They’ve both been using the same water, but the other one has been used frequently with no issue.
I think ChatGPT probably has the correct answer. Will test it, and if so will make sure to use both sides frequently in the future.

 

[Stu Jackson]

Larry, if you'd read my Rotten Egg link you'd have read that it covered way, way more than that. Please don't dismiss it because of the title. It includes an important "approved excerpt" from Peggie's book about plumbing system odors. Please give it a try.

Indeed one of them includes the suggestion to USE the system often. I got in the habit of using the hot water faucet even when cold to keep it movin'.

Heck, it even covers well water!!!

Thanks for the responses. No this is not a rotten egg issue.

 

[JoeWhite]

And I use hot water knob everywhere even when I do not need hot water. This bring fresh water to the water heater to keep it's water circulating at all times. If I have not used the water for 2 weeks, I use a 1 gallon bucket and fill from water heater to bring in new water to the water heater.

 

[thinwater]

With slight paraphrasing, this is the bleach treatment that a few have referenced above. It's from ANSI for RV and similar.

The RV code (ANSI A119.2 section 10.8) contains a simple procedure that is oft quoted and works very well. I’ve added a few details, but the bones of it come straight from the code and have been reviewed and accepted by the US Public Health Service.

• Turn off the hot water heater until finished.
• Remove any carbon canisters or micron-rated filters. Remove any faucet aerator screens. Wire mesh pump protection strainers should stay in place. The plumbing will very likely slough off a layer of bacteria during later flushing steps.
• Clean and remove the vent screen and flush the vent hose.
• Use the following methods to determine the amount of common household bleach needed to sanitize the tank.

A) Multiply “gallons of tank capacity” by 0.13; the result is the ounces of bleach needed to sanitize the tank. This is 1/8 cup of plain bleach (no fragrance) per 10 gallons.
B) Multiply “Liters of tank capacity” by 1.0; the result is the milliliters of bleach needed to sanitize the tank.

• Mix the proper amount of bleach within a 1-gallon container of water. This will provide better mixing and reduce spot corrosion of aluminum tanks.
• Pour the solution (water/bleach) into the tank and fill the tank with potable water.
• Allow some solution to escape through the vent, if safe and applicable (some boats use the vent as an overflow, while in some cases the vent is in the interior). This will sanitize the vent line.
• Open ALL faucets (hot and cold), allowing the water to run until all air is purged and the distinct odor of chlorine is detected. Leave the pressure pump on.
• The standard solution must have four (4) hours of contact time to disinfect completely. Doubling the solution concentration allows for contact time of one (1) hour.
• When the contact time is completed, drain the tank. Refill with potable water and purge the plumbing of all sanitizing solution. Repeat until bleach is no longer detectable.

 

[Scott NIelsen]

The attached file is a water purification table I use when refilling the water tank on my boat. hope it helps someone. I have laminated it and given it to fellow sailors at my marina.