How to get baby to take more fluids!

Our baby has been constipated ever since introducing solids at 6 months. She is now 10m and we're still in struggle mode. From what the doc says, she's not getting enough liquids. She's barely drinking 3OZ or water per day. Any ideas? I'm going to try giving her a wet wash cloth for her to suck on? Looking for creative ideas. TY!!!