Carry extra water and have the skills and tools required for obtaining and purifying additional water. Always carry at least one water bottle or collapsible water sack. Daily water consumption varies greatly. Two quarts (liters) daily is a reasonable minimum; in hot weather or at high altitudes, 6 quarts may not be enough. In dry environments, carry additional water. Plan for enough water to accommodate additional requirements due to heat, cold, altitude, exertion, or emergency.
Because water-borne diseases (bacteria and viruses) can be debilitating and sometimes lethal, you should always purify water before drinking.
Three popular methods of purifying water are:
1) Heat water to a rolling boil for at least 5-10 minutes; more if it is cloudy. This is the best method if you have sufficient fuel.
2) Chemically treat the water with chlorine bleach, iodine, chlorine or iodine pills such as Aqua Pure, Micro Pur, Halazone, etc. Treat water for at least 15 -45 minutes according to instructions. Longer if the water is very cold. This method kills most, but not all, micro-beasties.
3) Physically filter the water with a devices such as Katadyn, MSR, First Need, etc. Filtering down to 0.1 micron will eliminate viruses.
Other methods are Ultra Violet light irradiation, Activated Charcoal filtering, etc.
Pre-filtering the water to eliminate muddiness, suspended particles, dead bugs, etc. will greatly enhance the quality and appearance of the treated water. Even pre-filtering through a bandana or tee-shirt helps.
Note that none of these methods (except charcoal filtration) eliminates dissolved chemicals, such as heavy metals, pesticides, fertilizer, etc.
Jim Yuen, Sept 2008