The only way I know of to sterilize/decontaminate water and store it thus indefinitely is to use a reflux distillation process and drain the condensed water directly into sterilized/decontaminated glass containers. Done right, the distilled water can be stored indefinitely (or at least till the glass bottle wears out, let's say a practical limit of 500 years). The whole distillation/bottling process would need to be hermetically sealed.

Another way to store water indefinitely would be to freeze it. It won't eliminate pre-existing contaminants, but if you freeze it and put it in a sealed container, it should stay viable for a very long time.