This is what they say on the Big Ditch...
All water consumed or used for cooking should be purified. Research on the Colorado River and its tributaries indicate that increased sediment from flooding or other causes may pose a high risk to river users. The following water purification steps should be followed:
Use the main course of the Colorado River to collect water unless the river is quite cloudy from sediment.
Use side streams as a water source when the main river is laden with sediment and the side stream is running clear. Avoid the following tributaries because of inconsistent water quality: Paria River, Little Colorado River, Bright Angel Creek,
Garden Creek, Hermit Creek, Elves Chasm, Tapeats Creek, Deer Creek, Havasu Creek, and Diamond Creek.
Cloudy, sediment-laden water must be cleared before disinfecting. Settle overnight or use flocculating procedures (1 teaspoon alum per 5 gallons of water for drinking water). Decant the clear water into another container.
On the basis of a recent literature review, the Center for Disease Control and the Environmental Protection Agency recommended that water be rendered microbiologically safe for drinking by bringing it to a rolling boil for 1 minute; this will inactivate all major waterborne bacterial pathogens and waterborne protozoa.
Secondly, portable filters having a nominal pore size of 0.2 microns or less may also be used to remove bacteria and protozoan cysts. To assure removal of viruses, a disinfectant must be used in addition to the filter; current recommendations are 2 drops of chlorine per gallon after filtering. Settled water will extend filter life. Decant the clarified portion of settled water, filter, and disinfect with a product labeled for drinking water. Use the disinfectant according to the instructions on the label.
"Suppose you were an idiot, and suppose you were a member of congress; but I repeat myself." - Mark Twain