I have been saying for years that all that needs to be done for purifying water by boiling is to raise it to the boiling point and have received many skeptical looks in return. Here is a reasoned examination that explains exactly why this is true;
The fact is, with a water temperature of 165 degrees F (74 C) it takes just half an hour for all disease causing organisms to be inactivated. At 185 degrees this is cut to just a few minutes. By the time water hits its boiling point of 212 F (100 C) the water is safe. Even at high altitudes the time it takes for the water to reach a rolling boil and then cool means you can safely drink it.