Boiling will kill ALL the usual organic contamination, including viruses.

There are a few fungal and bacterial cooties that it won't kill, but they aren't generally water-borne. Clostridium botulinum bacteria, the active ingredient of botulism poisoning, is one of them, but it's found in food, not water.

"Boiling water is the best method for making water safe to drink. Boiling water as recommended will kill bacterial, parasitic, and viral causes of diarrhea. Adding a pinch of salt to each quart will improve the taste." From the Center for Disease Control

Sue