The safety of municipal tap water is defined by regulatory compliance, meaning the utility consistently meets all mandatory health standards set by federal and state agencies. Fresno’s water supply undergoes rigorous testing and treatment to meet these legal requirements, providing a baseline level of protection. This article examines Fresno’s water system, its regulatory status, the unique challenges posed by its Central Valley location, and steps residents can take to ensure water quality within their homes.
Overall Safety Assessment and Regulatory Compliance
The City of Fresno’s Department of Public Utilities consistently reports that the water delivered meets all state and federal drinking water standards. Compliance is mandated by the Safe Drinking Water Act and overseen in California by the State Water Resources Control Board. The city publishes its findings in the annual Consumer Confidence Report (CCR), detailing the water source, detected contaminants, and compliance status.
Receiving a passing compliance grade means the average levels of regulated contaminants remain below the Maximum Contaminant Levels (MCLs) established by the EPA and the state. However, meeting a legal standard does not always align with the most stringent public health goals. Health organizations often set Public Health Goals (PHGs) at concentrations lower than the MCLs to eliminate potential long-term health risks, especially for vulnerable populations.
The city manages compliance by blending water sources and taking wells with temporary high readings out of service to ensure the system-wide average remains compliant. If a specific well shows a spike in a contaminant like Nitrate or Arsenic, it is shut down or monitored until the running average returns to a compliant level. While this process ensures the utility avoids official violations, it can mask isolated incidents of higher contaminant concentrations within the distribution network.
Fresno’s Water Sources and Delivery System
Fresno’s water supply relies on a “conjunctive use” approach, drawing from both groundwater and surface water sources. Historically, the city relied almost entirely on the Fresno Sole Source Aquifer, a large underground water system. The city currently operates approximately 260 wells to draw water from this aquifer, which is part of the larger San Joaquin Valley Groundwater Basin.
To reduce the long-term strain on the aquifer and manage legacy contamination issues, Fresno has increased its use of surface water. This water is sourced from the Sierra Nevada snowmelt, delivered via the Kings and San Joaquin River systems, and conveyed through irrigation canals. Surface water requires extensive treatment at facilities like the Northeast and Southeast Surface Water Treatment Facilities, where processes such as coagulation, filtration, and disinfection prepare the water for consumption.
Blending groundwater and treated surface water is a strategy aimed at sustainability and water quality resilience. Groundwater is often vulnerable to contamination from surface activities, while surface water quality fluctuates seasonally based on snowmelt and weather conditions. The city also runs an aggressive recharge program, using surface water allocations to replenish the aquifer and manage groundwater overdraft.
Primary Water Quality Challenges
The geographical and agricultural context of the Central Valley presents specific water quality challenges for Fresno’s groundwater supply. The most persistent issue is the presence of Nitrates, stemming from agricultural fertilizers and septic systems that have leached into the aquifer. Nitrate levels in some wells have approached or exceeded the federal MCL of 10 milligrams per liter, which is concerning because high concentrations can cause methemoglobinemia, or “blue baby syndrome,” in infants.
Naturally occurring contaminants also pose a challenge, most notably Arsenic, a toxic metal found in the region’s soil and geology. Arsenic is a known human carcinogen; long-term exposure, even below the MCL, is linked to increased risk of various cancers and circulatory problems. Approximately 40% of Fresno’s groundwater wells have detected Arsenic concentrations, with some isolated wells temporarily testing above the 10 parts per billion (ppb) legal limit before being taken offline.
A third significant contaminant is 1,2,3-Trichloropropane (1,2,3-TCP), a synthetic chemical and probable human carcinogen used as a soil fumigant until the 1990s. Because 1,2,3-TCP is highly stable and slow to degrade, it persists in the groundwater. Although the state has set a regulatory limit of 5 parts per trillion (ppt), the chemical has been detected in multiple wells, requiring continuous monitoring and treatment. Emerging concerns also include Per- and polyfluoroalkyl substances (PFAS), which have been detected in some wells and are subject to new, stricter federal limits.
Steps for Improving Home Water Quality
For residents concerned about residual contaminants or who prefer water meeting the most stringent health guidelines, home filtration systems offer an additional layer of protection. The type of system needed depends on the specific contaminant of concern. For addressing issues like poor taste and odor, often caused by chlorine used in disinfection, a simple pitcher filter or a point-of-use carbon filter is effective.
Removing challenging contaminants like Nitrates and Arsenic requires advanced technology, such as a Reverse Osmosis (RO) system. RO works by forcing water through a semipermeable membrane fine enough to filter out up to 99% of dissolved solids, including Nitrates, Arsenic, and 1,2,3-TCP. These systems are typically installed under the kitchen sink to provide clean water for drinking and cooking.
Whole-house filtration systems, which treat all water entering the home, are another option, often utilizing multi-stage processes combining carbon filtration with other media. Residents should consult their Consumer Confidence Report to understand the contaminants detected in their area. If there are concerns about lead from older plumbing or localized contamination, a private water test can provide a precise measurement of the water quality at the tap.