What is the rule that sets MCL's for harmful chemicals?

The correct choice is the one that directly addresses the establishment of Maximum Contaminant Levels (MCLs) for harmful chemicals in drinking water. The Safe Drinking Water Act is the overarching federal law that enables the Environmental Protection Agency (EPA) to set these standards. Within the framework of this act, the Disinfection Byproduct Rule specifically focuses on regulating byproducts that form during the disinfection of drinking water, ensuring that levels of certain harmful chemicals are controlled to protect public health.

While other options refer to important regulations addressing different aspects of water quality and safety, they do not primarily set MCLs for a broad range of harmful chemicals like the Disinfection Byproduct Rule does in relation to disinfection processes. Therefore, understanding the role of the Disinfection Byproduct Rule is crucial in the context of maintaining safe drinking water and complying with health standards set forth by the EPA.