Install a reverse osmosis system in your house. However, not sure what to do about the pex piping though... Maybe run copper? Maybe there is an inert plastic?
Reverse osmosis can be also problematic cause it removes chemicals from water that are also useful. Maybe a less aggressive filtering method will do.
What chemicals could you possibly need in your water? There aren't any; the only thing you'd reasonably want in there are some minerals to make it taste good (totally pure water tastes pretty nasty actually). If you're talking about fluoride, the answer is simple: brush your teeth regularly and use dental rinse. You don't need it in your water. The only reason they ever did that was because too many people had terrible oral hygiene habits decades ago; people are a lot better about this these days, with quality toothpastes, motorized toothbrushes, flossing every day, fluoride rinses, etc.
There are inline units you can buy that add minerals back into the water, if thats what you mean by helpful chemicals.