hydrogen sulfide. I think a signal of bacteria that has made a home in your tank. I assume you're on a well? Also, since this is a vacation home, the water sits for a long time. To remove the bacteria, you'll need something like peroxide to the tank to kill the bacteria.

you might also want to drain the tank between uses.

If you do some web searches, you'll find other suggestions, like replacing the anode with one made of aluminum and zinc.

Thank you weed, I did a search with lots of results referring to changing anodes, and using hydrogen peroxide to flush. I'll give it a try next time down there. It's just odd that the 25+ year old tank I replaced never had that smell....?

If you suspect SRB colonization of your WH all you need do is raise the temp on the WH to 140 F for 2 hours. BE CAREFUL DURING THAT TIME AS THE HOT WATER WILL BE REALLY HOT. Then drain the WH and refill and reset the temp setting to a normal setting and you're good to go.

If the smell doesn't return then you solved the problem.

EDIT You don't want your WH set to 140 Ffor everyday use... only for the above procedure.

This post was edited by justalurker on Thu, Nov 21, 13 at 15:48

Thanks lurker! I'll try the super hot water method first, as that seems the easiest... come to think of it, the old water heater did produce much hotter water

After the HOT treatment you have to return the WH to a lower setting. You don't want your WH set to 140 F all the time

I ma with the idea of having an independent lab test the water. The anode rod may need changing to another material based upon water chemistry test.
given that this is a vacation home and we are talking about altering the tank temp setting, be aware that a tank water heater can be a great growth bed for Legionella bacteria. Tank water heaters should maintain a temp of 120F or higher. Be careful with this.