this is the one I got it's cheap and works great
https://www.amazon.com/gp/aw/d/B00MGSKSXI/ref=mp_s_a_1_6?ie=UTF8&qid=1469477640&sr=8-6&pi=AC_SX236_SY340_QL65&keywords=hydration+pack&dpPl=1&dpID=41A4GmoO1CL&ref=plSrch