This is simialr to the "Stinky Water" post on TBN from a couple of weeks ago, but with a different twist. I hope one of you may have an idea for me to try.
Our water comes from a well, goes into a cold-water tank (bladder, I think), then travels through a cartridge filter, through a non-functional UV filter, then to the hot water tank and the house.
About every four weeks, the water starts to smell, more noticable on the cold side, but on the hot as well. If I change the filter, it goes back to being great for another couple of weeks. One would assume that the water is just smelly and the filter fixes it, so when the filter is "done", it starts to smell again...EXCEPT: We also have a cold water hydrant out in the field that is tapped into the supply line to the house. So water coming out of the hydrant is before the filter. It doesn't smell at all.
The cold water tank is my suspect, but it is only about 18 months old as we had it put in when the well was dug.