The exact time required to accomplish this depends on altitude, the nature of impurity and several other factors. A safe general rule is at least 10 minutes, longer is by no means a waste except for fuel. If there is reasonable doubt water is contaminated, don't take chances even if in hurry. A great deal more inconvenience and delay can result from using just any water. This applies to water actually consumed and with equal gravity, to any water entering the human body.
Boiled water tastes flat.
Air and taste can be restored by pouring the cooled water back and forth between two buckets or by shaking it in a partially filled jar or canteen. If one is in hurry and has salt, just add a pinch of salt. Both can be made safe to drink without equipment. If time permits, such water can be filtered through a sieve of charcoal. This will both clarify and to a large extent, purify the water.