The water purification in China actually had the problem (in my opinion) of being too clean. Remove all the minerals and besides having no taste, the water will leach minerals out of the piping infrastructure, causing leaks.
This wouldn't cause a problem with salt water purification because you could let some of the water by-pass the filters, enhancing the taste.
Perhaps the best use for extra clean water filtration would be in recovering metals from the micro-electronic foundries. Or cleaning mining water from gold mines etcetera.