San Marcos, California Water Quality Report

The water quality in San Marcos, California has been comprehensively evaluated using data from the EPA's Safe Drinking Water Information System (SDWIS) and local water utility reports. Our analysis examines 8 distinct contaminants across multiple categories including inorganic chemicals, disinfection byproducts, microorganisms, and radionuclides. With an overall quality score of 45 out of 100 (Grade: F), San Marcos's water supply requires attention due to elevated contaminant levels.

Water Source and Treatment

San Marcos's primary water system, SAN MARCOS WATER SYSTEM, serves approximately 100,051 residents. The water is sourced from a combination of surface and groundwater sources. Groundwater is generally naturally filtered through soil and rock layers, though it may contain elevated levels of minerals and naturally occurring contaminants like arsenic or radon.

Contaminant Profile Overview

Of the 8 contaminants analyzed in San Marcos's water supply, 7 (88%) are present at safe levels below 50% of EPA Maximum Contaminant Levels (MCLs). 1 contaminant is detected at elevated levels between 50-100% of MCLs, warranting monitoring. No contaminants currently exceed EPA safety limits. The most common categories of concern in municipal water supplies include disinfection byproducts formed during the chlorination process, heavy metals like lead that can leach from aging infrastructure, and naturally occurring contaminants like arsenic or radium that vary by geographic region.

Regulatory Compliance Status

San Marcos's water system has a compliance history with 8 documented EPA violations. Currently, 1 violation remains unresolved and under active remediation. Violations can range from monitoring and reporting failures to actual exceedances of contaminant limits. Water utilities are required by law to notify customers of any violations that may affect health and to take corrective action to return to compliance.

Infrastructure Considerations

Water quality at the tap can differ from quality at the treatment plant due to distribution system conditions. Homes built before 1986 may have lead service lines or lead solder in plumbing that can contribute to lead exposure. Older galvanized pipes can harbor bacteria and release metals. Running cold water for 30 seconds to 2 minutes before drinking or cooking helps flush stagnant water from pipes. Residents in older homes should consider testing their water directly at the tap to assess any additional contamination from household plumbing, as EPA monitoring typically occurs at distribution points rather than individual residences.

Vulnerable Populations

Certain groups face elevated health risks from water contaminants and should take extra precautions. Pregnant women are particularly vulnerable as contaminants like lead and nitrates can affect fetal development, potentially causing developmental delays and birth defects. Infants and young children are at heightened risk because their developing bodies absorb contaminants more readily and are more susceptible to their effects; lead exposure in children can cause irreversible cognitive impairment and behavioral problems. Elderly individuals and those with compromised immune systems (including cancer patients, organ transplant recipients, and HIV/AIDS patients) are more susceptible to waterborne pathogens and may experience severe illness from microorganisms that healthy adults can tolerate. Individuals with kidney disease should be aware of fluoride and other mineral levels, as impaired kidney function affects the body's ability to filter these substances.

General Recommendations

Based on San Marcos's water quality profile, residents should consider the following protective measures: Installing a point-of-use water filter is strongly recommended given the current water quality score. Always use cold water for drinking and cooking, as hot water can contain higher levels of metals from pipes. Have your home tested if it was built before 1986 to check for lead plumbing. Review your annual Consumer Confidence Report (water quality report) from your utility to stay informed about local water quality trends. Pregnant women, families with young children, and immunocompromised individuals should consult healthcare providers about water safety precautions specific to their situation.