This got me thinking about our instant hot water faucet in our kitchen sink. I had been using this for my pour over coffee and tea however as this is a small tank under the sink this might not be a good option. Going back to my carafe to boil might be a safer bet. We do have a tankless water heater so water doesn’t stand there and new PEX pipes throughout so hopefully that helps however there could be biofilm forming in the PEX.