There are a lot of compliance warning labels that don't really mean anything. When I first visited California, I was pretty alarmed by the Prop 65 warnings plastered all over everything. Now I can't even see them anymore.
Propositions and people covering their asses is different than ignoring instructions for using a medical device. When it says "ONLY USE DISTILLED WATER", then that should give a reasonable person pause. It doesn't mean use any old water, it means use distilled water only.
I don't use distilled water because boiled tap water is close to free, and is more environmental than buying water that someone else distilled and then trucked around the country.
I'm not a full nettipot convert, but last year I did start using the squeeze-bottle version during pollen season, and was able to get over my extreme aversion to waterboarding myself. It takes a try or two, but eventually you get the hang of it and it actually feels quite nice. And if you haven't done it in a while, the snot you blow out the first time will be quite dirty and gross.