Save yourself the trouble of messing with water bottle's & mounts & go with a Camel Bak instead. If you think you need a lot of water buy one that can carry up to 102 ounces. You can gauge & carry only the amount of water you need per ride. Plus it will stay cold longer. Store the bladder with water in it in the refrigerator when you are not using it. Use the cleaning kit & disinfectant tablets at least once a year.

Here is one that will owrk well for you:
http://www.camelbak.com/rec/cb_prod....product_id=232