Getting stuck without clean water is not ideal. The Outback Plus OB-25NF is an emergency water filtration system that can give you up to 24 gallons of clean water every day. It gets rid of 99.99% of viruses and bacteria. These filters are good for 1800 gallons.
The Outback Plus is a gravity fed system. It can work with most fresh and moving water sources. You can find out more about it here.