You should bring a one-liter water bottle with you on the trek. We prefer that you purify water yourself using your own light-weight trekking water-filter, or that you bring and use your preference of chemical treatments such iodine.  Boiling personal drinking water is inefficient and uses scarce fuel. Along popular walking holiday and trekking routes (Annapurna, Everest, Mustang, and Langtang) bottled mineral water is available for purchase.