Are you looking for a way to purify your own drinking water in an off-grid or long term boondocking situation?
LDSPrepper reviews several popular filtering systems. Notably, most filtration systems require you start with pre-filtered tap water, so they're near useless in a boondocking situation when all you have available is river or pond water. His summary includes a clear winner.
(Note: Since he is reviewing only expensive commercial filters, he does not include an inexpensive DIY bio-sand filter