DD1 did the same thing at 6 months, I found if I pushed it, she bit or refused or didnt drink much, if she did I would just put her down and leave her. She would eventually come to me when she really wanted it and have a decent drink. I dont think they will intentionally starve themselves. I just perservered and eventually she went back to normal. If you are worried about dehydration have you tried sippy cups of water?