How much removal and/or inactivation of viruses is required in a water system from the raw water source to the first customer?

The requirement for virus removal and/or inactivation in a water distribution system is based on ensuring the safety and protection of public health. In many jurisdictions, the standard for the removal or inactivation of viruses in drinking water systems is set at a minimum of 4 log removal. This means that at least 99.99% of viruses present in the raw water must be removed or inactivated by the time the water reaches the first customer.

A 4 log removal effectively addresses potential health risks associated with viral contaminants, ensuring that the water supply is safe for consumption. This standard is grounded in rigorous public health policies to prevent outbreaks of waterborne diseases caused by viruses.

While lower levels of log removal, such as 2 or 3, provide some degree of virus reduction, they may not meet the robust safety requirements deemed necessary for potable water systems. A 5 log removal offers an even higher level of safety but may not be universally required or feasible for all water systems, hence the 4 log standard is the target for adequate protection against viral pathogens.