Carrying a couple of gallons of water is a lot of weight you don't need to haul, plus it takes up a huge amount of space in panners. Your best bet is to get a small camping water filter pump if you run into a situation where you can't find drinking water such as these:
http://www.purwaterfilter.com/hikguidpor.html These types of filters are so good you can take water from any stream, river, or lake and be drinking fresh wholesome water in minutes.
Then all you need is to carry 3 or 4 24 ounce bottles mounted on the frame so again not to take up panner space, and a 72 ounce Camelback.