>>910768A flask and a drop counter with bleach will suffice.
2 drops of bleach every liter of water (8 drops
every gallon) will disinfect water after 20 minutes.
You can filter the water through a natural filter (coal, sand, grass) or through a shemagh / bandana, then boil it and finally add 2 drops of bleach per liter and it will be as good as tap water.
A small flask of 250cc will let you purify around 2500 liters of water.
