Where I live the water is very hard, we dont have a water softener, and it's got all sorts of bad things in it (according to my neighbors). I've been using filtered water that you'd buy at the supermarket and it's getting kind of expensive. There is a place by where I live that will fill your bottles with RO (reverse osmosis) water for free. Is RO water good to use in fish tanks. If so would I need to add anything to the water to make it good for my FW fish or can i just add it like I was adding the water I bought?