How effective is log removal for viruses in water treatment?

Log removal is a measure commonly used to express the effectiveness of water treatment processes in removing pathogens, including viruses. Each "log" represents a tenfold reduction in the concentration of a target organism. Therefore, a 99% removal means that only 1% of the original concentration remains, while a 99.99% removal indicates that only 0.01% remains.

In the context of water treatment, achieving a log removal of 99.99% (or four logs) for viruses is considered optimal and is the standard for many treatment processes. This level of effectiveness ensures that the vast majority of viruses are successfully removed or inactivated, making the water much safer for consumption and use.

It is essential to recognize that while some disinfection methods may claim high levels of virus removal, factors such as contact time, temperature, and the presence of organic matter can significantly influence actual performance. Therefore, the standard of a 99.99% removal aligns with health and safety standards in water treatment practices, providing a high confidence level in the treatment process's ability to provide safe drinking water.