Cats are not big drinkers by nature. They evolved as desert predators who get most of their moisture from prey (which is 70% water).
They don't take in fluids so much by lapping up water, but by eating meat. So, if you feed a predominantly wet food diet, or raw, it is perfectly normal that they drink very little water. As long as you find nice big pees in the litter tray it's OK. It means they get sufficient fluids from their food. That's why it is so important to feed wet food... much more effective than buying fancy fountains.
Also, "stuff in the water" should not be harmful. If it was, there wouldn't be anymore cats around. :)