Oak Park Water Hardness & Quality Report (2026)

California Water Service Co - Westlake draws upon treated surface water purchased from Calleguas Municipal Water District to supply its roughly 19,494 customers in western Ventura County. The water originates from local creeks within the Calleguas Creek watershed, augmented by imported supplies from the State Water Project. Treatment occurs at Calleguas facilities, which process flows from Calleguas Creek and other sources. While there's no direct groundwater pumping for this supply, the system relies on a network of reservoirs and distribution mains to ensure consistent delivery to residents.

The Calleguas Creek watershed, a 350-square-mile area draining to the Pacific Ocean, cuts through Franciscan Complex mélange rocks from the Jurassic-Cretaceous period. These include greenstone and chert, which break down and release minerals. The Santa Monica Mountains contribute alluvial fans with gravels that help recharge shallow aquifers on the Oxnard Plain. Furthermore, runoff passes through areas with limestone and dolomite, dissolving these minerals and contributing to the water's hardness before it even reaches the treatment plant.

This level of hardness can lead to significant limescale buildup in your plumbing, water heaters, and dishwashers, potentially reducing their efficiency by 20-30% and shortening their lifespan. You might notice soap scum forming easily or feel dry skin after showering. To combat these issues, homeowners can perform regular vinegar descaling of appliances, install sediment pre-filters, and flush their water tanks annually. Many residents find that installing a whole-house water softener provides the most effective long-term solution. Local plumbers also suggest using bypass valves on outdoor lines to manage costs more effectively.