Birdman here is what I'd do. Write to your local water supply and ask for a guaranteed analysis. At least where I live they must mail it to you once a year. They must provide a copy at your request when you ask. It outlines what they consider to be safe parameters. It will tell you what they test for and what is present and in what volume say per gallon of water. They may use a formula like "per million". This means anything from a million drops to a million gallons the ratio will be the same. TDS is a reading of Total dissolved solids, typically per gallon. It will tell you how much copper is present, any can kill a reef. Copper can accumulate over time doing tap water water changes. It may not kill today but could over a year. Once copper enters the system it is nearly impossible to remove. It attaches to the rock, to the silicone, the sand etc... So doing water changes does not remove it, it actually adds to it each time. They will tell you what they use to "sterilize" the water be it chlorine or chloramine.
Personally I have an 8 stage 300GPD RO/DI unit that is attached to a 125g holding tank. I can guarantee EXACTLY what I put in the tank as I make it myself.
Not to mention it makes great coffee, tea, and Kool-Aid.