The small bag is called a HydroPack and it's manufactured by a company called Hydration Technologies, Inc. in Albany, Oregon. It requires no power, has no mechanical parts, and uses no purifying chemicals. It's a membrane that employs an advanced forward osmosis technique to remove bacteria, viruses, chemical poisons and other nasty stuff. It won't clog up, either, even if it's tossed into really muddy water, and making it work is so simple a child can do it.
Once the bag fills up, you simply sip the drinking tube and quench your thirst from a two-liter supply of a clean and safe Gatorade-like nutrient drink formulated to replace critical electrolytes lost during strenuous activity, including combat duty.
The patented membrane has pores that measure only about 3 to 5 angstroms in diameter (an angstrom is equal to one ten-billionth of a meter.) The smallest bacterium is about 2,000 angstroms wide, so it can't get inside; even the tiniest virus is at least 50 angstroms, making it ten times too large to pass through the forward osmosis action of the HydroPack, even if it says "open sesame."