Talk to your doctor because it's different for some babies. My doctor said it was fine at 4 monthes because my daughter had already double her birth weight. It's not necessary yet though.
6 months is when you can start giving a little water or juice. I bought juice and give her an ounce at a time every few days. I've not tried water yet. I just give her formula and solids.
Re: Water??
I give dd a few spoons every once in a while she loves it