Delaware Water Hardness & Quality Report (2026)

Delaware, Ohio, the Delaware County seat — a major central Ohio city north of Columbus, the birthplace of President Rutherford B. Hayes (the 19th US President — born in Delaware in 1822), home of Ohio Wesleyan University (a prestigious liberal arts university, founded 1842), a historic horse racing community (the Little Brown Jug — the most famous pacing race in harness racing history — is run at the Delaware County Fairgrounds each September), and a rapidly growing Columbus north exurban community — draws its municipal water supply from Delaware Lake on the Olentangy River via the City of Delaware Water Division. Water hardness in Delaware measures 238.5 mg/L — classified as very hard.

Delaware's very hard supply — notably harder than Columbus (168 mg/L) — reflects the Delaware County Olentangy River watershed's extremely calcareous Delaware Limestone geology. The Olentangy River (named for the Lenape — at Delaware Lake) drains directly through: the Devonian Delaware Limestone (the highly calcareous marine limestone directly named for Delaware, Ohio and Delaware County — nearly pure calcareous marine carbonate); the Devonian Columbus Limestone (highly calcareous); and the Silurian Niagaran Dolomite (highly calcareous dolomite). The Delaware Limestone namesake geology produces the very hard 238.5 mg/L at Delaware's municipal supply.

At 238.5 mg/L, Delaware residents face severe hard water challenges. Weekly descaling and appliance protection measures are strongly recommended. City of Delaware Water Division consistently delivers water meeting all Ohio EPA and federal EPA Safe Drinking Water Act requirements.