Any time you are concerned with water quality you should treat the water before consuming. In normal circumstances, municipal water in the United States and most developed countries is perfectly safe to drink. However, there are times when water quality cannot be trusted and treatment is strongly advised.

Water straight from natural sources such as rivers, streams or lakes. Water may be contaminated by runoff from surrounding lands.

Water from the tap when the water supply has been jeopardized by natural disasters such as floods, hurricanes, tornadoes or earthquakes. Physical breaches can allow external contaminants into water systems and power outages can disrupt water pumping stations, allowing water pressure to slow or become stagnant and creating risk of microbial contamination.

When local authorities announce a boil water advisory alert. According to the Center for Disease Control, in recent years, increased numbers of boil-water advisories have resulted from contamination of public drinking water systems with waterborne pathogens. Most notable was the outbreak of cryptosporidiosis in Milwaukee, Wisconsin, where the municipal water system was contaminated with the protozoan parasite Cryptosporidium parvum. An estimated 403,000 persons became ill.

When traveling to foreign countries with questionable water quality, especially Latin America, Asia, the Middle East and Africa. Even when locals are able to drink the water visitors may become ill. The Center for Disease Control provides a list of destinations and water safety recommendations listing UV water purification as a water treatment option when traveling.

In each of the situations listed above, there is the potential presence of a variety of microorganisms such as bacteria, viruses, protozoa, including giardia and cryptosporidium. These microbes make you sick by reproducing quickly and overwhelming your body’s immune system.