How do you get a baby to drink water?

ok my little girl is six months she is having trouble useing the bathroom, she stains for awile but when you change her diper she dosnt have anything except a little like a pebble soooo i think shes constipated, so my questions are...how can i get her to use the bathroom right or how do you make her drink water when she dosent like it....oh she dosnt like apple juice or any other juice