Where contamination can enter
Airborne contaminants, dirty collection surfaces, biofilm, plumbing materials, storage tanks and handling can all affect water quality. Clear-looking water is not proof of potability.
Use a treatment mindset
Public-health guidance for uncertain water emphasizes safe sources and appropriate treatment. CDC states that during emergencies people should use bottled, boiled or treated water when tap water is unavailable or unsafe, and that boiling is the best way to kill germs in water when boiling is appropriate.
Important limitation
Boiling or disinfection does not make water contaminated with fuels, toxic chemicals or radioactive materials safe. When chemical contamination is suspected, use a different safe source and follow local health guidance.