If a public water system uses a lake, river, stream or pond as it's water source, then it is regulated by the Surface Water Treatment Rule. This rule seeks to prevent waterborne diseases caused by viruses, Legionella, and Giardia lamblia. These disease-causing microbes are present at varying concentrations in most surface waters. The rule requires that water systems filter and disinfect water from surface water sources to reduce the occurrence of unsafe levels of these microbes.
This rule applies to all Public Water Supply Systems (community and non-community) using a surface water source (i.e. water open to the atmosphere and subject to surface runoff) or groundwater source under the direct influence of surface water.
For surface water systems, chlorine is monitored at the entry point and throughout the distribution system.