Monroe Water Hardness & Quality Report (2026)

Monroe, Louisiana, the Ouachita Parish seat on the Ouachita River in north Louisiana — the largest city in northeast Louisiana, home of the University of Louisiana Monroe (ULM), historically one of the world's largest natural gas deposits (the Monroe Gas Field — 'the Sargasso Sea of Natural Gas' in the early 20th century), and a major Ouachita River Valley agricultural and medical hub — draws its municipal water supply from the Ouachita River via the City of Monroe Water Division. Water hardness in Monroe measures 137.5 mg/L — classified as moderately hard.

Monroe's moderate hardness reflects the Ouachita River watershed's Gulf Coastal Plain calcareous geology. The Ouachita River above Monroe drains: the Arkansas Ouachita Mountains (Devonian–Mississippian Arkansas Novaculite and Ordovician Womble Shale — the calcareous-poor Ouachita Mountains chert and shale); the Louisiana Gulf Coastal Plain (Tertiary Claiborne Group — calcareous marine limestone, marl, and calcareous sand of the Gulf Coastal Plain Eocene sequence); and the Quaternary Ouachita River alluvial deposits (calcareous alluvial soil developed on the Gulf Coastal Plain). The Gulf Coastal Plain calcareous Tertiary marine terrain produces the moderate 137.5 mg/L at Monroe.

At 137.5 mg/L, Monroe residents encounter moderate scale accumulation. Faucet aerators and showerheads develop deposits after several months — monthly cleaning with citric acid solution is practical maintenance. City of Monroe Water Division consistently delivers water meeting all Louisiana DEQ and EPA Safe Drinking Water Act requirements.