Hollis Water Hardness & Quality Report (2026)

Hollis is a neighborhood in Queens, New York City, served by the New York City Department of Environmental Protection (DEP). Water is drawn from the Catskill and Delaware watersheds, feeding multiple reservoirs including Ashokan, Schoharie, and the Delaware system reservoirs. Water is treated at several DEP treatment plants before distribution across the five boroughs, including Queens. The service area encompasses all of New York City, with the DEP managing the full supply and distribution infrastructure for Hollis residents.

The Catskill and Delaware watersheds originate in the Appalachian Mountains, flowing through areas underlain by Devonian and Ordovician bedrock — including limestone, shale, and sandstone formations. These geological formations contribute dissolved minerals to the water supply, producing a moderately mineralized character. The watershed geology and treatment processes together shape the water chemistry delivered to Hollis, with carbonate exposures in the drainage area contributing moderate levels of calcium and magnesium.

As a moderately hard water supply, Hollis residents may experience moderate scale buildup in appliances such as dishwashers, water heaters, and washing machines. Soap and detergent effectiveness may be slightly reduced, though most households will not require a water softener. Regular maintenance of water-using appliances is recommended to manage mineral deposits. NYC DEP conducts extensive monitoring through reservoir stations and treatment plant testing; the water meets all federal and state standards for contaminants including lead and copper, with detailed quality data published annually in the NYC Drinking Water Supply and Quality Report.