Larkspur Water Hardness & Quality Report (2026)

Larkspur, California, receives its water from the Marin Municipal Water District (MMWD), a utility serving communities across Marin County. The MMWD draws approximately 75% of its supply from seven reservoirs nestled within the Mt. Tamalpais watershed, including Nicasio, Bon Tempe, Alpine, and Lagunitas. These reservoirs capture rainfall across a 160-square-mile area. The remaining water supply is imported through connections with the North Marin Water District, originating from reservoirs like Stafford Lake in Sonoma County. Water treatment takes place at the Jemez Springs and San Geronimo facilities, employing filtration, disinfection, and fluoridation. No desalination or artificial softening processes are utilized.

The primary watershed area is situated on the northern slopes of Mt. Tamalpais, part of the California Coast Ranges. This region is characterized by Franciscan Complex bedrock, which consists of metamorphosed oceanic sediments dating back to the Mesozoic era. These rock types have a low solubility for hardness-causing minerals. Supplemental groundwater is drawn from shallow alluvial deposits found in valleys like Novato and San Rafael, which lie atop this ancient formation. The water's inherent softness is a direct result of rainwater percolating through these silica-rich, non-calcareous geological materials, leading to a very soft water supply overall.

Because Larkspur's water is naturally soft, residents won't experience issues with scale buildup on plumbing fixtures, pipes, or appliances such as water heaters and dishwashers. Consequently, no special maintenance related to water hardness is required, and installing a water softener is neither necessary nor recommended, as it could potentially remove beneficial minerals. You can expect sparkling glassware and efficiently operating fixtures without any intervention. The MMWD consistently meets federal drinking water standards, with annual reports confirming compliance, including effective corrosion control measures and the absence of lead or copper exceedances. Recent tests also show no PFAS detections above regulated limits, and trace disinfection byproducts like TTHMs remain well below maximum contaminant levels.