Gilroy Water Hardness & Quality Report (2026)

The City of Gilroy Public Works Department operates the municipal water utility serving approximately 58,000 residents in Gilroy, Santa Clara County, California (ZIP 95020). The utility sources 100% of its supply from local groundwater wells tapping the Llagas Basin Aquifer, with no surface water imports. Water is extracted from wells on the valley floor with treatment limited to disinfection for microbial control, as the groundwater is naturally low in organics.

Gilroy's groundwater originates in the Llagas Subbasin, part of the broader Santa Clara Valley Groundwater Basin. Recharge comes from local rainfall infiltrating Quaternary alluvial deposits derived from granitic and sedimentary rocks in the adjacent Santa Cruz Mountains and Diablo Range. These alluvial formations overlie older Tertiary bedrock and contain limestone and mineral-rich layers that release dissolved calcium and magnesium into the groundwater, resulting in a hard supply rich in these minerals.

Hard water in Gilroy promotes significant scale buildup in pipes, water heaters, dishwashers, and washing machines, reducing efficiency, shortening appliance lifespan, and increasing energy costs. Soap lathering is poor, leading to higher detergent use, potential dry skin, and dull hair. Regular descaling of fixtures and annual flushing of water heaters is recommended. A water softener is strongly advised to protect appliances and plumbing. Annual reports confirm compliance with federal and state standards; sodium levels average 26.56 ppm (range 17–58 ppm) and lead and copper testing shows no MCL violations. No PFAS data is noted in available reports.