Chloride is one of the major inorganic ions in water and wastewater, and can impart a salty taste to drinking water at elevated concentrations. Chloride concentrations also indicate the degree to which ocean derived saltwater has moved into the freshwater portion of the upper estuary. DRBC has adopted criteria and monitors chlorides to ensure water quality in the upper estuary remains suitable as a source of drinking water.

One important metric for understanding the importance of salinity concentrations in the Delaware Estuary is the location of the 250 mg/L chloride concentration based on drinking water quality standards originally established by the U.S. Public Health Service, also known as the "salt line." The salt line's location fluctuates along the tidal Delaware River as streamflows increase or decrease in response to changing inflows, which either dilute or concentrate chlorides in the river.

The seven-day average location of the salt line is used by DRBC as an indicator of salinity intrusion in the Delaware Estuary and is tracked as part of the commission's flow and drought management program, which focuses on controlling the upstream migration of salty water from the Delaware Bay during low-flow conditions in basin rivers and streams. As salt-laced water moves upriver, it increases corrosion control costs for surface water users, particularly industry, and can raise the treatment costs for public water suppliers. Salinity levels also affect aquatic living resources.