If you're looking to buy a water treatment system that can remove bacteria from water in an emergency situation, I would recommend using an emergency preparedness portable water filter.
Straw water filters, bottle filters and gravity-fed water filters are all good options for emergency preparedness, as they don't need water pressure or electricity to operate.
Make sure that the filter you choose can remove bacteria, as not all filters can (see above). You can read my full guide on emergency preparedness water filters if you're interested in learning more.