If you want to keep i natural, get an infuser bottle. You can add fruit, or veg like cucumber, even fresh mint.I also add a ¼ cup of water and loads of ice to my protein shakes.
I use multiple things, propel is good, they make a flavored water, the squirty mio type, kool aid flavors are great , and of course my big fav is vitamin water zero, no carbs no sugar and lots of extra vitamins and minerals to help your new body.