Unfortunately, I don't know the specific technologies by name or their cost in particular.
I can make an analogy to 40 years ago, or more, when we discovered extensive contamination by chlorinated solvents, which were widely distributed in our society in large and small communities. They're commonly used in tool and dye manufacturing and by dry cleaners. It meant that small communities would have these chlorinated solvent-type plumes.
Once you discover the nature and the extent of the problem with these very toxic chemicals, and that they're in your drinking water supply, the first thing is to stop using them or mitigate their use. Then, I suppose, you need to immediately worry about the quality of the water that's being purveyed to the individuals as a drinking water source and those treatment technologies.