It is recommended that you fill your bottles with natural spring water available free of cost while traveling to Yamunotri. During trekking you wont find any dearth of local taps en route. But it is advisable to fill your bottles with water from your starting point of the trek. Once you reach the temple, descend down to bank and have your heart's fill of the pure glacier waters of Yamuna. The intoxication and satisfaction is indescribable.