I've just been diagnosed with a ubiquitous pulmonary bacteria called MAC commonly found in tap water and that requires a 0.2 micron filter. It's smaller than other bacteria and treatment is long and difficult. Reinfection is common.

I want to obviously avoid reinfection if I clear it which requires me to reduce exposure as much as possible. I live alone on a 9th floor condo with basement central boilers so an external whole house water filtration system is out-- Ultra Violet and RO systems are not ideal either. For the bath shower, there are hospital grade 0.2 micron showerhead filters. Cold water needs in kitchen and bathroom can happen with an ultrafiltration system filtering down to 0.2.

The dilemma is that it survives dishwashing cycles because the water doesn't get hot enough and, therefore, dishwasher contents not bacteria-free even after the wash. So my thought is to filter my kitchen cold water line w/ ultrafiltration. That comes out bacteria-free. Can I feed that filtered water into an under-counter, tankless water heater that can then feed the dishwasher? The tankless version appeals to me as an added safety to prevent colonization should any slip through. Thoughts?

  • 1
    Consider a new dishwasher with a built-in heating element that uses cold water (and can provide adequate heat to sanitize things, too, using the built-in element.)
    – Ecnerwal
    Aug 26, 2023 at 2:40
  • 1
    Does that even include dishwashers with a heat sanitize cycle?
    – KMJ
    Aug 26, 2023 at 5:58

1 Answer 1


With a 0.2 micron filter, the pressure loss and therefore the water flow will be very low.

While, theoretically you can feed the dishwasher and the tap/faucet, practically, it is unlikely to work.


  • As mentioned by @Ecnerwal, for your health's sake get a dishwasher that will heat the water to kill the bacteria.
  • Consider a multistage filter or a hospital grade filter for your tap and shower.
  • Also look at reverse osmosis type filters. I have never used them, so I am not sure about their performance.
  • For drinking, you could look at evaporative/condensing type gadgets.
  • That sounds easy enough. Thanks to you all!
    – Michael
    Aug 26, 2023 at 19:09

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