Dan, you shouldn't need to give a bf baby water at all, but usually people start to introduce water sometime between 6 and 12 months to start getting the baby used to it. Both of my boys started drinking water regularly at about 7 months, although in my case this was probably more to do with them starting day care than anything. It doesn't really matter which way you go, the water isn't neceassary but it won't hurt either.