[RAVEN]

Many LFS sell RO water at a reasonable price. I used Tap water to fill my 120g FOWLR tank but use RO water to replace evaporation loss. I have had no problems doing this. I would not recommend this for a reef tank. I strickly use RO water in my reef tank and have my own RO system producing over 25g per day. Tap water quality varies from city to city. You have to know the water quality of your area, some water contains heavy metals, copper, nitrates, ect.. If you do use tap water use high quality carbon and a heavy metal absorbing resin such as purigen or cuprisorb by seachem. I would aslo test the water for phosphates and use a phosoban or some other resin. You may also want to consider using Red Sea's salt called Reef Crystal's which they claim has a heavy metal binding agent. The best thing to do however would be to use RO water.