It really depends on where you live, i.e. the source. There may be very little, or there may be a lot.
Finding out what is actually
in your local tap water also depends on where you live.
For example, I can find
pages of analyses of everything found in my own local tap water, but I find almost nothing (specifics) on tap water
anywhere in the UK other than blanket statements that it's "safe". (They do admit to purification chemicals, calcium & magnesium salts, microplastics, and lead)
So they said (it's "safe") about the water in
Flint, MI and elsewhere.

(It's made us a little skeptical here in the US)
...until I found this:
Do you know what’s in your tap water? (UK specific)
I'm surprised distilled water is expensive and hard to get there, but we're not talking about supplying your entire household—we're talking about enough for a lizard. Another option to distilled is Reverse Osmosis (R.O.) which AFAIK is a fancy type of filtering. I can get distilled for about $0.69US per US gal.
Can anyone give a figure on how much distilled water their chameleon enclosure goes through on a weekly or monthly basis? (dripping, misting, fogging, plants combined)
I'd chalk it up to cost of keeping the little booger, but we use it for so many other things, it'd be hard to separate out.