You can achieve a WHO approved method with a coke bottle and sunlight. Put water in a PET bottle, then leave it in the sun for 6 hours. It is now safe to drink. If it's overcast or the water is murky, you need 2 days.
As a bonus, coke bottles (or any fizzy drink bottle) are ideal as a water container for hiking; lightweight, capable of holding pressure (so they can withstand being squashed in a pack), and surprisingly resilient when falling from a height (compared to purchased bottles). And they cost nothing.
As a bonus, coke bottles (or any fizzy drink bottle) are ideal as a water container for hiking; lightweight, capable of holding pressure (so they can withstand being squashed in a pack), and surprisingly resilient when falling from a height (compared to purchased bottles). And they cost nothing.