There are no laws or regulations for tap water quality in the US.
Different locations have different tap water contents. In many areas, tap water can change in quality / contents from season to season.
I would recommend the use of an RO water purification system. If this does not fit into your current plans, then the use of reliable TDS meter is a must.
RO membrains wear out. They need replacement on a regular basis. Depending on the quality of the tap water and the amount run through an RO membrain relates to the life of the filtering ability of the unit.
Many hobbyists ask about marine salts that once mixed into a clear working solution, then some months later have concerns that the salt mix they are using are now producing a slightly cloudy solution. After some exhange of information, it is revealed that the RO water they are purchasing is from an outlet where the RO membrain from the seller needs changing.
A TDS meter will allow you to understand the quality of the water you are buying.
Here is a link with some information about RO filtration.
Aqua Craft®, Inc. Reverse Osmosis
Some brands of marine salts can vary in their phosphate content from time to time. It is always best to use a marine salt that is consistently made from high purity ingredients.