UV is effective at inactivating bacteria, viruses and protozoa, such as Cryptosporidium and Giardia, which may be present in water supplies from potentially all sources. Many people believe that well water is pristine, glacier water is pure and municipal water is treated to safety standards specified by regulatory bodies. While all of this is generally true, even these ’good’ sources of water may be contaminated. Groundwater quality can be degraded by failing septic systems, animal farms and many other sources. Groundwater in aquifers is continuously moving, which results in variable quality. It can test good today but fail tomorrow. People who fall sick tend to blame it on the food they ate or some other explanation because they believe their water is safe. Areas where microorganism contaminants are highest are at the base of mountains where pure water from mountain streams is collected. Yet the water picks up contaminants on its journey down the mountain that can create the need for disinfection.
Cryptosporidium and Giardia protozoa are more evident in drinking water supplies. The occurrence of Cryptosporidium parvum in drinking water sources is recognized as a significant threat to private and public water supplies throughout the world (Rose et al., 1991; Lisle and Rose, 1995; Messner and Wolpert, 2000). Water treatment plants usually cannot guarantee the removal of all Cryptosporidium because oocysts are very small (four to five micrometers in diameter), and are resistant to chlorine and most other disinfectants.1 It is for this reason that many municipal treatment plants are installing UV systems.
The most challenging water source is the dug well, where runoff is an issue. As runoff enters the well, it can carry with it such contaminants as surface animal waste and septic drainage from the aquifer.
Municipal water can be deemed perfectly safe when it leaves the treatment plant. Nonetheless, Boil Water Alerts (BWA) happen frequently as a result of the unexpected. Many times the BWA is issued 24 to 48 hours after the contamination is detected. Residential POE UV can be a primary barrier to protect people from contamination in a well that has failed a water test, and it can be inexpensive insurance to others who think water is safe all the time, but want to be sure that their family is fully protected.