A relevant excerpt from Zen Backpacking...............


http://zenbackpacking.net/WaterFilterPurifierTreatment.htm

The US military uses Chlor-Floc water purification tablets which uses aluminum sulfate as a flocculating agent.

Flocculating agents allow for removal of suspended solids in water by promoting rapid clomping and sedimentation of fine particles suspended in water. This sediment is then easily removed by straining the water through a cloth or by siphoning or pouring off just the clear water. This isn't a "filter" treatment in itself but allows for the removal many suspended solids to improve clarity and taste of water as well as decreasing the amount of treatment (chemical/filtration/heat/radiation/etc) needed for your water.

Flocculating and coagulation can remove 60–98% of microorganisms, heavy metals, and some chemicals and minerals from water.