Distilled water and glass bottles are the way to go. You can get a small distiller for your home relatively cheaply.
Or one powered by solar panels? :)
And people have made spreadsheets to help with cloning specific mineral waters with the exact blend of salts, e.g.:
https://blog.khymos.org/2012/01/04/mineral-waters-a-la-carte...
A 16oz bottle of San Pellegrino has 20mg of sodium. How can such a small difference in sodium intake (and other minerals) have a meaningful influence on electrolyte levels?