Yes, there are substances that slip through, but it works well enough for most cases that it's probably fine. Otherwise you get into weird edge cases like "what if there are prions in the water?!?" or whatever.
Heavy metals are a big problem, especially from cheap brass fittings common in outdoor water hoses.
Indoor plumbing, by contrast, uses copper and/or plex tubing and so there’s near zero risk of metal poisoning (caveat on cheap plex fittings- don’t do that.)
It's not.