I work for a developer and we have an ongoing problem. Our homeowners are complaining of a smell in mostly just one of their sinks. A black gunk can mostly be found in the traps at these sinks. They are on city water and almost all of these homeowners do have water softners. We have tried numerous things including changing sinks, changing traps, changing water heater anodes, adding vents to the sink in question. After doing research online I am guessing that this is sulfur residue (the black gunk) in their traps. But how is it getting there? Can it be something that the water company is using in their plant?

Answer: There many causes of black staining, but the common ones are from the presence of sulfur, manganese, or bacteria.  It is unlikely that sulfur or manganese would be prevalent in a municipal water supply, as they would be removed at the point of distribution to protect the delivery system.  In addition, you would not be noticing the black material and odor at only one point in the home – it would be evident at all sinks in the home (to varying degrees due to differences in water usage).

This is something that we have run into before.  Occasionally, a homeowner will complain about an odor coming from only one or two sinks in the home (mostly from a bathroom sink).  This seems surprising, as it can happen on municipal water supplies containing chlorine.  An easy conclusion to reach is that the odor cannot be caused by a bacteria, as the chlorine in the piping would destroy it.  However, this is not always the case.  Collect both hot & cold water in a container directly from the faucet at the offending sink.  Remove the sample from the room, and smell it.  If it does not have any odor, go back to the sink, and run the water again.  If the odor is now present, it is likely that a bacterial growth has developed in the sink trap (this can happen fairly quickly), and the action of fresh water passing down into the drain blows a “sulfur like” odor of decomposition back up into the room.  The concentration of chlorine contained in the municipal water is not high enough (and there may not be sufficient contact time with the bacteria) to destroy it completely in the drain.

There are other possibilities, but periodic chlorination of the drain should resolve the problem.  As to why this only happens in some localities, we do not quite understand.  Probably has something to do with area humidity, temperature, atmospheric pressure, chlorine concentration of the water, etc. – who knows?  Maybe one of our other contributors has some experience with this situation?

I installed a softener about six months ago and have been using potassium chloride instead of sodium chloride as a regeneration agent. The softener seems to be working fine, but requires regeneration more often than I would expect based on calculation from water hardness, usage and softener capacity. I understood that KCl and NaCl were essentially the same as far as softener setup goes. If that’s not the case, should I extend the recharge cycle or just lower the trip limit for a recharge? Thanks!

Answer:  Sorry for the late reply – busy week here!  To some extent it depends on what type and quality of cation exchange resin you are using, but assuming that your water softener resin is a generic “high-capacity” type, it’s not always the case that sodium and potassium chloride are equivalent.   Potassium chloride (KCL) adheres more strongly to the water softener resin, and this can reduce the exchange efficiency when compared to sodium chloride (NaCL), requiring more potassium chloride used per regeneration.  For most good quality water softeners, you won’t need to make any adjustment.  However, if you are using potassium chloride, and also trying maximize the capacity of your softener, a good rule of thumb is to use an additional 4 pounds of salt per cubic foot of resin per regeneration.  Hope this answers your question.