Longmont Water Hardness & Quality Report (2026)

The City of Longmont Utilities Department serves over 98,000 residents in the Front Range area of Boulder County, Colorado. The drinking water supply is entirely surface water drawn from streams, lakes, and reservoirs in the North St. Vrain Creek and South St. Vrain Creek watersheds, originating from mountain snowmelt and rainfall. Water is treated at city-managed facilities using conventional processes for total organic carbon removal, disinfection, and metals monitoring, with rigorous annual testing detailed in the Consumer Confidence Report.

The watersheds originate in pristine mountain areas; the North St. Vrain is primarily wilderness with minimal human impact, while the South St. Vrain may be affected by runoff from abandoned mines. Geological features beneath the Front Range include limestone, gypsum, and mineral-rich sedimentary deposits from ancient inland seas; however, snowmelt-driven surface water has limited contact with these formations. This results in a very soft water character with low dissolved mineral content shaping the overall chemistry.

As very soft water (21 mg/L), Longmont's supply causes minimal scale buildup in pipes and appliances, reducing maintenance needs for water heaters, dishwashers, and washing machines. Soaps and detergents perform efficiently without excess usage. No water softener is needed; mineral levels of approximately 1–2 grains per gallon do not warrant treatment. The 2023 Water Quality Report shows alkalinity averaging 29.7 ppm and aluminum averaging 29 ppb from treatment byproducts and natural erosion. Lead and copper compliance is maintained under state monitoring. Chromium (hexavalent), TTHMs, and radium exceed some health advocacy guidelines but remain within legal limits; treatment involves conventional TOC removal and disinfection.