Which process does not contribute to the reduction of pathogens in drinking water?

The process that does not actively contribute to the reduction of pathogens in drinking water is storage. While storing water can help improve the overall quality due to sedimentation and the natural die-off of some microorganisms over time, it does not actively kill or remove pathogens. Instead, it simply allows the water to sit, which means that unless specific measures are taken, pathogens may remain in the water.

On the other hand, chlorination is a method used to disinfect water by adding chlorine, which effectively kills or inactivates harmful microorganisms. Filtration involves passing water through a barrier that can remove contaminants, including pathogens, depending on the filter's design and capabilities. Boiling water is an effective method for killing bacteria, viruses, and parasites, as the high temperatures involved in boiling will destroy these harmful organisms.

Thus, while storage might lead to some incidental pathogen reduction over time, it does not have the direct, active impact that the other processes have in ensuring the water is free from harmful pathogens.