I think at that age, it's fine if she's just having breastmilk on demand. You might consider starting to offer a sippy or open cup of water to play with here and there, like if you're outside on a warm day (when it doesn't matter too much if she gets wet) or in the bath if she's sitting up well, but she probably won't really drink much or any at all yet. We really didn't start offering water until about 9 months, and even then, my daughter couldn't really even hold or lift the cup well (I'd have to help support some of the weight). She would play with it in the bath though. It was maybe close to about 12-13 months when she actually started to drink from it a bit more regularly at meal times.