Water Softeners and Air Filtration Systems - Filter exit subject to contamination?

I have an (Omni) under-the-sink water filter which has been in place for ~7 years. The line from the filter to the (dedicated) faucet is a plastic tube which is noticeably discolored: a grayish brown.

I wrote to the manufacturer and they said the discoloration is entirely from carbon fines which got dislodged from the filter.

My wife thinks it is from bacteria growing in the line. Her reasoning: once the water is filtered, there is no significant chlorine in the exit line. Further, when I replace the filters, air gets into the tube. Bacteria travels on airborne dust, so it is possible that it could be getting into the line.

Does anyone know generally if there is concern about contamination of filter exit lines because they are not chlorinated? I understand that the filtered water itself is not contaminated, but again, air in the line can introduce foreign substances. It only takes one microscopic bacterium to start a major colony.

P.S. Note that replacing the exit line is not a simple matter because on this particular model of faucet, the line is integrated into the faucet. So I would have to replace the entire assembly. Read: significant expense and effort.

And anyway, I want to know if the new line would get contaminated again.

The discoloration of the line is NOT caused by dislodged carbon. Strange for a manufacturer to claim this. It may be from iron content or other elements in the water. Bacterial film may also be there.

To sanitize the system (single filter system, right?), remove the filter and put a little bleach in the housing and reconnect without filter. Let sit for a while and drain it through the faucet in spurts and later let it drain till you don't smell bleach anymore.

Replace with new filter. Do this occasionally.

Andy Christensen, CWS-II

Thanks, Andy. It's a double filter, but I assume the same will apply: just take out both filters and toss some bleach in both compartments. I'll give that a try.

Do you perchance have any sort of documentation to support this? I'd like to take the manufacturer to task... :)

The discoloration of the line is NOT caused by dislodged carbon. Strange for a manufacturer to claim this. It may be from iron content or other elements in the water. Bacterial film may also be there.

To sanitize the system (single filter system, right?), remove the filter and put a little bleach in the housing and reconnect without filter. Let sit for a while and drain it through the faucet in spurts and later let it drain till you don't smell bleach anymore.

Replace with new filter. Do this occasionally.

Andy Christensen, CWS-II

I tried this procedure, but with a lot of bleach. I slowly pumped bleach through the line for at least three hours.

The line is still discolored. I am sure there is nothing living in there at the moment, but... wondering now if maybe Omni was right? I would have thought the bleach would have, um, bleached out the bacteria if that's what it was.

The discoloration of the line will not go away. It is stained. You may have a little iron or manganese or another substance in your water that the filter is not designed to remove.

Replace the line and see if happens again over time. I wouldn't worry about it.

Andy Christensen, CWS-II