Adenovirus control in small drinking water systems: risks and strategies

Many small drinking water treatment systems disinfect using only ultraviolet light, which provides minimal adenovirus inactivation at common doses. There is uncertainty in jurisdictions around the world about whether such practices should be accepted by regulators, or whether there is a need to specify a treatment target for adenovirus. A preliminary objective of this study was to determine whether adequate adenovirus information exists to conduct a meaningful quantitative microbial risk assessment (QMRA). The study then applied the QMRA framework to draw conclusions about whether there is justification to regulate adenovirus, and to identify weaknesses in those conclusions. A thorough review revealed that the quality of data available to conduct the analysis was poor. Using the (limited) data available, the QMRA suggests that adenovirus may pose risks similar to other viruses that are regulated. A lack of information about the concentration of adenovirus in source waters makes it difficult to propose a compelling evidence-based argument either for or against the need to require adenovirus treatment. Furthermore, management of risk from waterborne adenovirus should take into account an endemic rate of infection from non-waterborne exposures that appears to obscure accepted levels of waterborne risk.