Plastic Mineral Water bottles are a great problem in the hills.

They are non-returnable, non-biodegradable and cause considerable pollution.

Come to KEEP's Travellers' Information Centre in Thamel for Mineral Water bottle refills while you are in Kathmandu

Or buy IODINE water purification tablets for your Treks. Chlorine- or silver nitrate-based tablets don't kill the 'Nepal nasties' - iodine does, but the tablets are hard to obtain elsewhere in Nepal.