From what I have read on the subject, a lot of the bottled water that is sold on the market is simply filtered tap water, bottled and sold as spring water, or whatever label they want to put on it.
I have a water distiller, but it takes it all day long to purify a gallon of water, so we also use filtered water for most of our water needs.
I used to give my dogs plain old water from the faucet, but you read about so many contaminants in water nowdays, that I always give them the same water that we drink. When it is not, I add ice cubes to keep it fresh for them.
I also add about a third of a capful of apple cider vinegar to keep their Ph balanced and prevent parasites.