In order to get 8 glasses a day I add a few slices of apple or cucumber or sprigs of mint to my water. It helps to keep me interested in the water instead of getting bored of the taste. I also drink it through a straw which helps me drink more, faster without realizing. Get lemon wedges at restaurants instead of soda or iced tea and avoid the packets of flavor since there is a lot of added sugar. Keep it natural and experiment!
You can flavor water with pretty much anything - melon, any citrus (I love limes) just get creative for a subtle flavor!