Why is establishing an MCL for pathogenic organisms considered impractical?

Establishing a Maximum Contaminant Level (MCL) for pathogenic organisms is considered impractical largely because there are no practical and universally applicable tests available for their presence. Testing for pathogens involves complex procedures that may require advanced technology and specialized equipment, which can be time-consuming and costly. Additionally, the presence of pathogens can fluctuate, making it difficult to accurately gauge their concentration in various water sources over time.

Furthermore, pathogens encompass a wide range of microorganisms, including bacteria, viruses, and protozoa, each requiring different testing methodologies. Because of these factors, monitoring water for pathogenic organisms through an MCL poses significant challenges, making it less feasible compared to other contaminants that can be assessed with established testing methods. Thus, while the goal of protecting public health is paramount, the practical limitations around testing for pathogens lead to difficulties in setting and enforcing MCLs specifically for these organisms.