Another thing I never quite understood was how bacteria thrive in purified water anyway, to the point where they can form biofilm. Where do they even get the necessary nutrients?
It doesn't take much for bacteria or fungi to start growing on previously filtered water once it's open to air. Just take a glass of filtered water and leave it out for a few weeks. Some glasses won't grow anything. Others will have all sorts of things floating on the surface.
Pasteur is credited for formalizing this knowledge when he figured out that if you used a crooked necked flask to store media, it reduces the chance of airborne contamination.
Once bacteria form a biofilm, it could make it more difficult for any chlorine or UV light to disinfect or sanitize the surface. The bacteria have formed a sort of protective bubble.
Mycobacteria are particularly good at resisting various antibiotics because they have a thicker than average cell envelope. Mycobacterium tuberculosis is another bug in this family.
Anyway I have not found any suitable answer for cleaning the water pipes after these strip everything out of the water filter systems, and whilst it shouldnt be a problem if you have copper pipes throughout the house because copper kills most bacteria and some viruses, hence copper water vessels from the past, if you have the new plastic flexible piping in the house, cleaning will almost certainly be required.
Penicillin based antibiotics when they are broken down in the liver become penicillamine and this causes the body to release lots of copper into the blood stream, so how much is that having an antibacterial effect on the body? Plus copper is also needed for interleukin-6 which kills alot of cancer, so if doing lots of penicillin antibiotics, your risk of cancer could go up if your dietary copper intake is not high! Something the medical professionals dont tell you!
So something like what the pubs use to flush their pipes leading up from the barrels and kegs should do it for cleaning the water system pipes after the water filter, but like I say, I havent found anything satisfactory from these household water supply filter people. Certainly copper pipes are best though, and if doing some DIY, dont leave any flux on the pipe because in damp cold conditions, condensation reacts with the flux and it causes tiny pinholes to form in the pipe. A good plumber will clean their pipes down to stop this from happening otherwise you get minute water leaks that can get worse very quickly.
UV-C is the main disinfecting UV light source, but you dont want to go near it because UV-C destroys pretty much anything which is why most of it is blocked in the upper atmosphere.
I know hospitals use it to clean wards and rooms, but it will destroy materials much more quickly, ideally hospitals would clean a ward and room like normal to remove ground on dirt and then use the robots that move around shining UV-C all over the place.
FWIW, the main sanitizer used for kegs is the same thing used in restaurants for the standard "three sink" cleaning system (last dip is in sanitizer). Star San is the main brand name. It's a mild acid and it's both cheap and readily available. It works basically by denaturing proteins, which any acid will do, but the specific one is chosen to be harmless and relatively tasteless as well as easily clinging to surfaces to give extra contact time.
I'm not sure it would be a good idea to use it, though, as it might eat away at some plumbing fixtures (e.g. galvanized pipe).
If you did, you'd want the non-foaming variety (which is not called star san... Saniclean, I think? Same brand, either way).
https://finance.yahoo.com/news/insane-golden-chamber-contain...
scroll down to the "Terrifyingly pure water" section for a fun read on how fun really pure water can be.