I suppose that having a small amount of silver or even just copper touching the water can seriously prolong its shelf life, so to say.
Also, putting sterilized water into airtight sterilized containers, as normally done with beer, works well. Carry a can of Liquid Death with you instead of a can of Bud, the weight is the same.
... Because the process of making beer consists of boiling the wort!
But if you can boil water to make beer, you can just, well, boil water to drink.
People have known since antiquity how to make water potable.