Basically, we recognize that tap water today (such as is provided by city water) is supposed to be normal water that has been filtered and santizied etc and made acceptable for drinking. But rather than aiming to produce water that is actually good for drinking, the water treatment plants at best aim to produce water that is not too bad for consumption. They determine that water is not too bad if it only has very small quantities of all the bad things that are filtered out. And I would like to imagine that they are usually correct that most of those things in such small quantities are not harmful in a glass of water, but like any other pollution, although a healthy person can handle small amounts as it is built to be able to handle, yet it is not built to handle that everyday and all the time, throughout all stages of life, etc.
On top of the bad things that are mostly filtered out, the water treatment plants will add poisons to santize the water, such as chlorine. Fluoride also is added in an effort to medically treat the teeth of the population.
To defend this poisoning of water, some will speak out of both sides of the mouth, saying that, on the one hand, “there is not enough poison added for it to affect your body”, and yet on the other hand “there is just posion enough added to be effective in santizing the water.” It is clear to me that if it is a quantity effective in santizing the water then it is going to be effective in “sanitizing” my body as well, to at least some extent, which I don’t want. The same goes for fluoride: if it’s a quantity allegedly effective in treating my teeth, then it’s a quantity I shouldn’t be swallowing.
In general Fluoride in particular is very controversial and apparently untrustworthy, as shown at links such as these:
http://www.livingwhole.org/why-i-turned-off-the-tap-said-no-to-fluoride/
Information about the lethality of Fluoride in toothpaste, such as in Colgates for Kids toothpaste (for example, that consuming just half of a children’s sized tube of toothpaste is enough to kill a 2 year old).
http://fluoridealert.org/studies/acute01/
Also, a couple articles about how questionable tap water already is:
https://healthywildandfree.com/6-convincing-reasons-to-never-drink-or-bathe-in-tap-water-ever-again/
https://diversehealthservices.wordpress.com/2016/01/21/4-reasons-you-shouldnt-drink-tap-water-even-if-you-dont-live-in-flint-mi/
A not-quite-reassuring article by WebMD about how safe tap water is supposed to be (the best I could find), along with some other information.
http://www.webmd.com/women/home-health-and-safety-9/safe-drinking-water
So I think that using some kind of actually effective water filter or distiller is necessary for ordinary drinking water, unless you don’t have to deal with city water because you have a good natural source, such as a spring or well or rainwater system or a cistern of some sort. For dealing with city water, the two processes that I have the most confidence in are reverse-osmosis and distillation. In general it all ‘boils down to’ what you want to do and don’t want to consume on a regular, daily basis.
I use this water distiller. It is built in such a way that the water water, once distilled, never comes in contact with plastic.
https://www.amazon.com/Megahome-Countertop-Water-Distiller-Collection/dp/B00026F9F8
Job 36:26-28
Behold, God is great, and we know him not,
neither can the number of his years be searched out.
For he maketh small the drops of water:
they pour down rain according to the vapour thereof:
which the clouds do drop and distil upon man abundantly.