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General Activities => Main Message Board => Topic started by: Ken Heyman on August 25, 2010, 06:37:22 AM

Title: hot water "rotten egg" odor
Post by: Ken Heyman on August 25, 2010, 06:37:22 AM
I hadn't turned on the hot water faucet in either the head or galley for a few weeks. Recently when I did, there was a pronounced rotten egg or maybe  hydrogen peroxide (?) odor. I ran all of the hot water out of the system and did this a second time yesterday after an engine run. It does appears to be abating. What chemical process could cause this kind  of odor in our hot water tank or elsewhere in the system? It doesn't smell anyting like the usual standing water odor.

---just curious,

Title: Re: hot water "rotten egg" odor
Post by: Ken Heyman on August 25, 2010, 06:42:43 AM
BTW-Stu did mention this phenomena a couple of years ago:

Another trick on hot water heaters:  if you get in the habit of using the hot water faucet, even when there is no hot water, you'll keep gunk moving through the heater and perhaps reduce the amount of scale buildup on the coil; it also reduces any chance of rotten egg smells from the hot water side
Title: Re: hot water "rotten egg" odor
Post by: Ken Juul on August 25, 2010, 07:43:49 AM
Hopefully one of the Chemists on the board will correct me, but I always thought heating the water removed or defeated the cholorine allowing sitting water to turn skunky.  Skunky water can happen on the cold water side also, but much more prevelant on the hot water side.  Using the water is the key, like Stu suggests, use the hot faucet as much as possible.
Title: Re: hot water "rotten egg" odor
Post by: Steve Sayian on August 25, 2010, 08:00:42 AM
I add a little bleach to the tanks when I fill them.  Takes care of the problem as we don't drink the tank water.

My hair is a lot grayer after vacation, but at my age, I don't care!!!  ;-)

Title: Re: hot water "rotten egg" odor
Post by: jmnpe on August 25, 2010, 08:30:30 AM
As a person who has a water well for our only household water supply, this is a subject with which I am quite familiar. The "rotten egg" smell is set in motion by the presence of even low levels of sulfur in the water supply. The smell comes from hydrogen sulfide gas released as a byproduct of sulfur eating microbes that also are present in the water. Elevated temperatures accelerate the rate at which the microbes can consume/convert the sulfur, and the longer the microbes are able to "work" on a confined volume of water, the higher the concentration of hydrogen sulfide becomes in that water.

There are really only about 3 easy solutions to the problem.

1. Keep the water moving ( i.e. - limit the time that the microbes have to operate in a "trapped" volume of water ) so that the concentration of hydrogen sulfide can't reach "stinky" levels. This works pretty well on the cold water side of our home water supply.

2. Heat the water to about 170 F or higher for a period of time. This will kill the microbes and prevent the chemical process from starting. This works pretty well on the hot water side of our home water system with normal daily usage, and we have really hot water.

3. "Shock" chlorinate the water. This will also kill the microbes. This requires higher levels of chlorine initially to be effective, so you wouldn't want to do this just before you leave the dock for that over-nighter on the water. This is our method of last resort on our home water system.

None of these solutions are comprehensive over longer periods of time of limited or no water usage. It requires constant effort, although on a boat with a limited amount of water to deal with, it is probably easier to control than in a household water system.

There is a lot of information on this subject online if you search something like "rotten egg well water".

Happy microbe hunting  :thumb:


Title: Re: hot water "rotten egg" odor
Post by: Ken Heyman on August 25, 2010, 09:16:05 AM
thanks much John! (and all)---I've been educated and humbled.

Fair Winds,

Title: Re: hot water "rotten egg" odor
Post by: Ken Juul on August 25, 2010, 09:38:54 AM
My marina has well water....I avoid using it.  First trip of the spring is to a dock with city water.  I also bring a 10 gals of city water to the boat each visit in water jugs to replenish.  The chemicals in the city water do a great job of keeping the smell (microbes?) away.  I also use Peggy's recommissioning recommendations each spring, copied from a post Stu did a while back.


This is regularly re-posted by Peggie Hall on the website.  I copied it for my own files and reprint it here.  Evidently, adding a little bit'o'bleach everytime isn't the appropriate thing to do.  Read on...


Title: Recommission the system at least annually

"This is all it takes to keep onboard water safe, and tasting/smelling as good as any that comes out of faucets on land: Fresh water system problems--foul odor or taste--are typically caused by allowing water to stagnate in the system. Although most people think only in terms of the tank, the plumbing is actually the source of most foul water, because the molds, mildew, fungi and bacteria which cause it thrive in damp dark places, not under water. Many people—and even some boat manufacturers—believe that keeping the tanks empty reduce the problem, but an empty water tank only provides another damp dark home for those “critters.”   There are all kinds of products sold that claim to keep onboard water fresh, but all that’s really necessary is an annual or in especially warm climates, semi-annual recommissioning of the entire system—tank and plumbing.

The following recommendations conform to section 10.8 in the A-1 192 code covering electrical, plumbing, and heating of recreational vehicles. The solution is approved and recommended by competent health officials.  It may be used in a new system a used one that has not been used for a period of time, or one that may have been contaminated. Before beginning, turn off hot water heater at the breaker; do not turn it on again until the entire recommissioning is complete.  Icemakers should be left running to allow cleaning out of the water feed line; however the first two buckets of ice—the bucket generated during recommissioning and the first bucketful afterward--should be discarded.

1. Prepare a chlorine solution using one gallon of water and 1/2 cup (4 oz) Clorox or Purex household bleach (5% sodium Hypochlorite solution ). With tank empty, pour chlorine solution into tank. Use one gallon of solution for each 5 gallons of tank capacity.
2. Complete filling of tank with fresh water. Open each faucet and drain cock until air has been released and the entire system is filled.  Do not turn off the pump; it must remain on to keep the system pressurized and the solution in the lines
3. Allow to stand for at least three hours, but no longer than 24 hours. 4. Drain through every faucet on the boat (and if you haven't done this in a while, it's a good idea to remove any diffusion screens from the faucets, because what's likely to come out will clog them). Fill the tank again with fresh water only, drain again through every faucet on the boat.
5. To remove excess chlorine taste or odor which might remain, prepare a solution of one quart white vinegar to five gallons water and allow this solution to agitate in tank for several days by vehicle motion.
6. Drain tank again through every faucet, and flush the lines again by fill the tank 1/4-1/2 full and again flushing with potable water.

People have expressed concern about using this method to recommission aluminum tanks. While bleach (chlorine) IS corrosive, it’s effects are cumulative.  So the effect of an annual or semi-annual "shock treatment" is negligible compared to the cumulative effect of holding chlorinated city water in the tank for years. Nevertheless, it's a good idea to mix the total amount of bleach in a few gallons of water before putting it into either a stainless or aluminum tank. People have also expressed concern about the potential damage to rubber and neoprene water pump parts. Again—the cumulative effect of carrying chlorinated water is far more damaging over time than the occasional “shock treatment.” And it’s that cumulative effect that makes it a VERY bad idea to add a little bleach to each fill.  Not only does it damage the system, but unless you add enough to make your water taste and smell like a laundry, it’s not enough to do any good.  Even if it were, any “purifying” properties in chlorine evaporate within 24 hours, leaving behind only the corrosive properties.

An annual or semi-annual recommissioning according to the above directions is all that should be necessary to keep your water tasting and smelling as good as anything that comes out of any faucet on land.  If you need to improve on that, install a water filter. Just remember that a filter is not a substitute for cleaning out the system, and that filters require regular inspection and cleaning or replacement. To keep the water system cleaner longer, use your fresh water...keep water flowing through system. The molds, fungi, and bacteria only start to grow in hoses that aren't being used.

Before filling the tank each time, always let the dock water run for at least 15 minutes first...the same critters that like the lines on your boat LOVE the dock supply line and your hose that sit in the warm sun, and you certainly don't want to transfer water that's been sitting in the dock supply line to your boat's system. So let the water run long enough to flush out all the water that's been standing in them so that what goes into your boat is coming straight from the water main.

Finally, while the molds, fungi and bacteria in onboard water systems here in the US may not be pleasant, we're dealing only with aesthetics...water purity isn't an issue here--or in most developed nations...the water supply has already been purified (unless you're using well-water). However, when cruising out of the country, it's a good idea to know what you're putting in your tanks...and if you're in any doubt, boil all water that's to be drunk or used to wash dishes, and/or treat each tankful to purify. It's even more important in these areas to let the water run before putting it in the tank, because any harmful bacteria will REALLY proliferate in water hoses left sitting on the dock. "
Title: Re: hot water "rotten egg" odor
Post by: Stu Jackson on August 25, 2010, 11:15:07 AM
Thanks, Ken.  We used to have Peggie's complete writeup from another website on our site, but when she wrote her book we were requested to delete it, fairly I believe.  Now that she's a regular here, and has posted that so many times on, I'm sure it's OK with her to "reprint" it here.

I see all sorts of homemade brews on other websites and really appreciate hearing, again, how to do it right from a true expert.

Should be easy to find in the future, too, search on "recommission."  Interestingly enough, it gets lotsa hits on exactly this topic! :D
Title: Re: hot water "rotten egg" odor
Post by: Peggie Hall on August 25, 2010, 03:32:06 PM
I'm glad to have you post the fresh water recommissioning instructions.  Btw...the ratio of bleach to water works out to a quart of bleach to 50 gal. water. However, if it's ONLY the HOT water that smells like rotten eggs, it may be the sulphur content in the water...or a failed anode in the tank.  Here's a bit of "water heaters 101" from the tech services manager at Raritan:

Anodes are included in the water heater of glass-lined steel tanks to protect the inside of the tank against corrosion from acids in the water, stray electrical currents, etc. Glass lined tanks, when the water heater is being built, are heated up red hot. Then glass powder is sprayed inside the tank and it adheres upon contact. However, it doesn't cover every single crack and crevice inside the tank - it should, but in actual practice, it doesn't. The purpose of the anode is to protect those spots inside the tank that have not been glass-covered from rusting away prematurely. The anode is eaten away, rather than the tank being eaten away. Kind of a backup to the glass lining.

The anode is a magnesium rod, about 3/4" in diameter that is attached to the inside of the hot water "out" nipple, via a plastic coupling. It is electrically isolated from the fittings and from the tank. It extends all the way across the inside of the tank, stopping just short of the other side. There is an iron rod in the center of the magnesium that supports it, the iron being stronger than the magnesium. As the magnesium is eaten away and the iron rod exposed, there's a chemical reaction between the water, the iron and the magnesium that causes the "rotten egg" smell. Replacing the anode and flushing out the tank will usually make the foul smell go away.

Replacing the anode in a glass lined tank is an inexpensive job that takes all of 20 minutes.  But unfortunately not all marine water heaters have glass lined tanks...the cheaper ones have anodized aluminum tanks. When the anodizing wears off, as it must in time, the only cure is new water heater.
Title: Re: hot water "rotten egg" odor
Post by: Stu Jackson on August 25, 2010, 04:03:55 PM

Do you know if the Seaward heaters are made with anodes?  I don't recall seeing that in the instruction manual when I redid my hot water heater hoses:,3769.0.html (,3769.0.html)  with photos, and discussion of heater with others.

Followup August 2014 - Seaward makes an anode, but it's an add-on extra that replaces the drain valve.
Title: Re: hot water "rotten egg" odor
Post by: Ron Hill on August 25, 2010, 04:05:34 PM
Guys : The best way to eliminate the hydrogen sulfide (rotten eggs) smell is to start by cleaning out the water tanks and hoses as Peggy has mentioned.

I carry it one step further -- (charcoal) filter the water when you fill the tanks!!  Then add a cap full of bleach to each the tanks 1 cap per 25 gal of water.  
There is a definite reaction of the PVC hoses causing the H2S smell.  That's why I changed the type hose and rerouted the head sink hoses out from the warm/hot engine compartment.  Wrote a Mainsheet article about What, Why and How I did that !!

I drink, brush my teeth and make coffee from the water stored in the on-board tanks.  My 1st Mate likes to use the filter on the galley faucet, but still uses the on-board water!!

The Water heater has an aluminum core (a friend did an autopsy on his old one). I know of no anode and it's not the culprit - the PVC hoses are!   

A few thoughts  :idea:
Title: Re: hot water "rotten egg" odor
Post by: horsemel on August 25, 2010, 07:23:00 PM
When you fill the tanks, go to WalMart and buy a RV hose filler filter.  It goes on the hose and you run the water through into your tank.  It is cheap and keeps the crud from the marina lines out of the tank.
Mark Mueller
Title: Re: hot water "rotten egg" odor
Post by: Ron Hill on August 26, 2010, 06:40:04 PM
Guys : Go to Lowe's and look at their water filters and make your own - that's where I got mine. Simply adapt it with a garden water hose fitting on the inlet side and a 1ft length piece of hose on the other end.  They have the disposable charcoal filters.  Cheap insurance
As mentioned it will keep the sand etc. out of your water tanks.  A thought
Title: Re: hot water "rotten egg" odor
Post by: Mike and Joanne Stimmler on September 11, 2010, 04:10:49 PM

Here's a picture of what I think Ron is talking about. I got mine at Home Depot and it works really well.

Title: Re: hot water "rotten egg" odor
Post by: Ron Hill on September 11, 2010, 05:11:44 PM
Mike : Correct, Mine looks similar and does the same thing. 
I put a female hose adapter on the one end and a male 1/2" hose barb on the other end.  It's stored next to the propane box in the aft lazerette.  Only need to change the filter element once a year, as I don't use the filter if I'm taking on "city" water.  A thought