Getting my daughters to drink water? add colouring? flavored water?

well i have had many problems getting my girls to drink water. all 4. so i tried adding a little food colouring. just so it dont look like water. well unfortunately they expect it all the time now with their water. is it alright for them to have it. they have about 2 sups of the water a day. instead of the coloured water. which wotks. would it be okay to give them flavoured water?