Pollution can affect ice, snow, water in streams and in shallow wells causing these water sources to be unsafe. Even clear streams can have parasites in them. Unpolluted water must be boiled to assure complete destruction of any dangerous organisms. Properly stored water is the safest in an emergency. If you have to use water from an unknown source or of unknown quality, be aware that the following methods of purifying water do not guarantee the safety of the water but will reduce the risks involved.
Boiling water is one of the safest methods of water purification.
It should be boiled for at least 20 minutes to insure that bacteria are killed. Boiling does not remove pollution. The boiling process will make the water taste flat since some air has been driven out. To add back the oxygen and to improve the taste, pour the water several times from one container to another. Another method is to pour the water into a closed container and vigorously shake it.