Baby is 20 weeks, can she have a little watered down juice?

She is about a week shy of five months, after her usual 5 ounce breast milk around 6 I give her a few bites of baby food. Testing it like they say to, lately she seems a little dehydrated (her soft spots sinks a little) and I can't get her to drink water no matter what I do, can I give her really watered down juice. This started a few weeks ago, before I gave her the baby food, so I know that is not the cause. I mean like a teaspoon of juice to a few oz of water.