I messed up with my daughter when she was small, and only gave her milk or juice, until a really hot day when she was 2, and I was worried that juice would give her diarrhea and milk would turn her stomach.
I walked to the Family Dollar 3 blocks away, and got a couple squirt guns. I rinsed them out really well, and then filled them up with cold water from the fridge. I showed her how fun it was to drink from the water gun. When she got a little older, she would refuse to drink if it wasn't milk or juice in HER cup but she would drink from MY giant cup of ice water. Finally, I told her if she wasn't thirsty enough for her own water, she just wasn't thirsty. It only took about 3 hours before she caved.
I didn't make the same mistake with my son. He's loved cold water since he was off the bottle and onto a sippy cup.