What is the log inactivation requirement of Giardia according to the surface water treatment rule?

The log inactivation requirement of Giardia according to the Surface Water Treatment Rule is set at a level of 3. This means that water treatment processes must be capable of achieving a 99.9% reduction in the presence of Giardia cysts in the treated water to ensure that it is safe for consumption.

The rationale behind this requirement is based on the risk associated with Giardia, a waterborne pathogen that can cause gastrointestinal illness. The Surface Water Treatment Rule was established to protect public health by requiring water utilities to implement effective treatment practices that minimize the risk of these pathogens in drinking water. By targeting a log inactivation of 3, the rule reflects a significant safety margin to account for potential variabilities in source water quality and treatment effectiveness.

It's important to note that while higher log inactivation levels may be indicated for other pathogens, particularly viruses, Giardia's specific requirement takes into account its biology and the risk it poses relative to other pathogens that can be present in surface water supplies.