Well Water in Marin County: What to Test and Why

Groundwater in Marin County contains arsenic, boron, and chloride. Contaminant levels here are low and do not exceed EPA health standards.

These contaminants come from the rock and soil that make up the coastal basins beneath Marin County. Arsenic and boron occur naturally in the local rock layers, while chloride enters groundwater from saltwater that borders the coast and from historical salt intrusion in some areas.

Groundwater in this county is moderately hard and contains elevated sodium. Sodium concentrations are high here because the coastal rock layers and nearby ocean water release this mineral into the groundwater system. Most wells in Marin County show these moderate hardness and sodium levels.

Wells in this county do not show analytes exceeding EPA health standards. However, arsenic, boron, and chloride are present in the groundwater and warrant your attention. These elements can build up in your body over time and affect your health, which is why testing your specific well is important.

County well water tends to have elevated sodium and dissolved minerals that create practical challenges. You may notice a salty or mineral taste in your water. The moderate hardness can cause scale buildup in pipes and appliances, shortening the lifespan of water heaters and dishwashers over time.

We recommend testing your well to find out what contaminants and minerals are actually present in your water. Every well is different, and your water may have higher or lower levels than what is common across the county. Testing is the only way to know what you need to treat. A comprehensive minerals and metals panel typically costs $200 to $400 and can guide you toward solutions like reverse osmosis systems or ion exchange softeners.