Not just for your fish but have you requested a water report yet? I just did. Contact your water supplier, apparantly its law that you can ask for a report free. Find the chart that lists contaminents. It should have a column that shows acceptable levels of components and actual levels.

We have a charcoal filter attached to our main tap for drinking water but it isn't the tap I use for the fish water. As expected there are nitrates in my fish water. I am going to the DIY tomorrow to get the recommended kit that checks for bacteria levels (yep they're in tap water too) lead, copper and nitrates. I believe in the US the kit is called Watersafes All in One- ($20) has anyone used this kit?

I know lead poisoning and high levels of copper can cause 'swimbladder' /vertical swimming, airsac malfunction & actually internal poisoning at certain levels and want to find out more about this. Anyone have more info on potential dangers of leeching chemicals I'd like to hear your experiences.

I have the water report for my water, which is how i know that the nitrate levels in it can be as high as 18. there are a lot of things in water that i didnt know were there.
I dont have any info as to the dangers though, but I have been using water from the same source for 11 or so years even though i have moved house, it is the same supply.