I was going to suggest slices of lemon and mint. I fill a jug with lemon slices and just keep topping up the water you only need to change the lemons everyday. Good on you for drinking more water. The more you drink the more you want to drink and your body will start absorbing it better soon too. If you are drinking a large amount at once it can tend to go straight thru so be sure to sip here and there as well, that way it's easier for your body to absorb. I would stay away fro the flavoured waters because of the added ingredients, but you could start with one 750 flavoured water and one plain and then increase the plain water and decrease the flavoured water slowly too.

Also a slice of lemon in boiling water and drinking it as hot as you can handle it a brilliant way to kick the liver into gear and process any toxins in your system.