How many log removals are required for viruses?

To ensure the safety of drinking water, regulations typically stipulate certain levels of pathogen removal or inactivation. For viruses, a 4 log removal is commonly required. This translates to a 99.99% reduction in the concentration of viruses present.

Achieving this level of viral reduction is crucial because viruses can be significantly more resistant to treatment methods compared to bacteria or other microbial contaminants. A 4 log removal effectively minimizes the risk of viral infections, making drinking water safer for public consumption. This standard is consistent with guidelines from health organizations and regulatory bodies aimed at protecting public health.

In contrast, lower log removal levels—such as 2 log (99%) or 3 log (99.9%)—may not adequately ensure the complete inactivation of all virus types, leaving potential health risks. Even a 5 log removal, while it offers higher safety assurance, is typically considered beyond the minimum necessary requirement for viral pathogens under most regulations. Hence, the requirement of 4 log removal reflects a balanced approach to achieving high safety standards in water treatment processes.