Usually leave a tip if the service was pleasant and quality. The standard amount is 10 % above the receipt of the invoice. But do not forget that the staff make very little money, and their main income - tip.
Mains water is chlorinated and is fine for brushing teeth. However, bottled water is advised for drinking, especially outside Tirana. Brucellosis and tuberculosis are present in Albanian dairy cattle. Unpasteurised milk and homemade cheese should be avoided; however, in cafes and restaurants the milk is always UHT, and therefore safe.