I used tap water once cause someone was given poor advice in a bitchy way and my ex really didn't want me to use tap water and I did to prove a point. I got pretty sick
Tap water is good enough to drink but when you think a bit stomach acid and things probably kill the many microorganisms in the tap water.
Also you can cotton fever from not using sterile cotton. Why? Because it's like grown in soil and what not and not like qtips and cigarettes and its the same idea with heroin and stuff you always want to use a filter cause the same idea. You cab botulism, tetanus, I'm pretty sure anthrax was in soil too
Your introducing things right into your blood stream when these things could possibly make you sick with out mainlining it to your heart and brain. Could get meningitis which is a brain infection and they don't recommend diving in like in lakes and stuff because that can happen if dirty water shoots up your nose.
I never use filters
But ya I hope the people saying tap water is fine has actually done it because it's not recommended and I know why (Also I'm a highly self destructive person and self harming I did through drugs, that's one of the only reasons I did it and to prove a point)
Also if your going to use like puddle water or something ya they would say tap water is better but go to a harm reduction place and get supplies. Also like somethings are highly contagious and like MRSA is a thing and you can spread that but ya