Mendota Water Hardness & Quality Report (2026)

The City of Mendota Water Department draws its entire supply from groundwater wells that tap into the San Joaquin Valley aquifer. This aquifer system, located in Fresno County, California, is fed by recharge from the Sierra Nevada foothills and local irrigation return flows. Water undergoes a treatment process that includes pre-oxidation with chlorine, filtration, and disinfection using hypochlorite before reaching the approximately 11,404 residents of Mendota. The utility's administrative offices are at 643 Quince Street, and they can be reached by phone at 559-655-3291.

Mendota's groundwater originates within the Central Valley aquifer system, specifically the unconsolidated alluvial aquifers of Fresno County. As water percolates through thick sequences of Quaternary-age sediments, including sands, gravels, silts, and clays deposited by the ancestral San Joaquin River, it leaches calcium and magnesium ions from mineral fragments like limestone, gypsum, and dolomite. These minerals are embedded within the alluvial deposits and older Tertiary formations such as the Etchegoin and Tulare Formations, contributing to the water's hard character over centuries of flow within this endorheic basin.

Homeowners in Mendota will likely notice significant scale buildup in pipes, water heaters, dishwashers, and washing machines due to the water's hardness, which can reduce efficiency and shorten appliance lifespans. Common signs include white spots on glassware and soap scum in showers. Regular descaling with vinegar, using high-efficiency detergents, and employing rinse aids specifically formulated for hard water are helpful maintenance practices. Given the water's character, installing a water softener is strongly recommended to protect appliances and mitigate these effects. The 2026 water quality report assigned the supply a grade of B (80/100).