Manganese in San Fernando Valley Tap Water: What the EPA Secondary Standard and LADWP Data Show

What Is the EPA Secondary Standard for Manganese?

The EPA regulates manganese under the Secondary Drinking Water Standards, codified at 40 CFR Part 143.3. The Secondary Maximum Contaminant Level (SMCL) for manganese is 0.05 mg/L, equal to 50 micrograms per liter (50 ppb). Secondary standards exist separately from primary Maximum Contaminant Levels (MCLs). Primary MCLs are enforceable health limits. Secondary standards are advisory, addressing aesthetic effects: taste, odor, color, and staining. A utility is not in regulatory violation if manganese in its distribution system exceeds the SMCL.

California adds a layer above the federal secondary standard. The State Water Resources Control Board has established a Health Notification Level for manganese at 0.5 mg/L (500 ppb). When a utility detects manganese above that level, it must notify customers. The Health Notification Level is ten times higher than the EPA aesthetic advisory SMCL. Verify the current Health Notification Level at waterboards.ca.gov, as notification thresholds are subject to revision.

How Manganese Enters San Fernando Valley Tap Water

Manganese is a naturally occurring metal found in soil and rock formations throughout California. It enters drinking water through two primary pathways in the San Fernando Valley. First, local groundwater: LADWP draws from the San Fernando Valley Groundwater Basin, which is managed under adjudication. Groundwater in the SFV basin comes into contact with manganese-bearing mineral deposits through geological weathering, a process documented across California groundwater systems by the USGS National Water Information System. Second, imported surface water: LADWP purchases treated water from the Metropolitan Water District, which blends water from the Colorado River Aqueduct and the State Water Project. Each source has a distinct mineral profile, and the blend ratio shifts seasonally based on MWD allocation decisions.

The blended nature of SFV tap water means that manganese concentrations at any individual tap depend on which sources LADWP is drawing from at that time, how the local groundwater contribution has changed, and what treatment the water received at the treatment facility. The annual Consumer Confidence Report reflects distribution system averages, not point-of-use readings. As noted in the SFV water quality source breakdown, seasonal blending variation affects mineral profiles across the service area.

What LADWP and Las Virgenes MWD Report

LADWP is required to report detected manganese levels in its annual Consumer Confidence Report under the Safe Drinking Water Act. The LADWP 2024 Consumer Confidence Report documents measured contaminant levels across the full distribution system. Because manganese is regulated under the secondary advisory standard rather than a primary MCL, LADWP is not required to treat the water to fall below the SMCL, only to report what it detects. Verify the specific detection figures in the current CCR at ladwp.com, since annual figures change with source blend, treatment upgrades, and groundwater conditions.

Homes in Calabasas, Agoura Hills, and Westlake Village served by Las Virgenes Municipal Water District receive water from the same MWD system and face a similar source-blend profile. LVMWD publishes its own Consumer Confidence Report at lvmwd.com/water-quality. CCR figures from both utilities reflect distribution system test points, not tap readings at individual addresses.

Regulatory Reference: Manganese Standards at a Glance

Secondary standards under the Safe Drinking Water Act are advisory, not enforceable. A utility that detects manganese above the EPA Secondary MCL of 0.05 mg/L is not in federal violation and is not required to remove manganese from the distribution system. California layered a notification requirement on top of the federal advisory: the State Water Resources Control Board Health Notification Level of 0.5 mg/L requires utilities to notify customers when detections exceed that threshold. That is ten times higher than the EPA aesthetic limit, which is why many SFV households receive water that is technically within the federal advisory range but still causes visible staining on fixtures and laundry.

Two additional reference points appear in public health guidance. The EPA Office of Water has published a Health Advisory for chronic manganese exposure at 0.3 mg/L (300 ppb), which provides separate guidance for long-term drinking water exposure and is distinct from the aesthetic SMCL. The World Health Organization guideline of 0.08 mg/L (80 ppb) reflects the taste and odor detection threshold at which manganese becomes perceptible to most people, rather than a health-based enforceable limit. Verify current thresholds at epa.gov/sdwa and waterboards.ca.gov before relying on any specific value for treatment decisions, since regulatory levels are subject to revision by rulemaking.

Testing for Manganese at Your Tap

Consumer Confidence Reports published by LADWP and Las Virgenes MWD reflect distribution system averages drawn from multiple test points across the service area, sampled at fixed locations that regulators have approved for compliance monitoring. These figures do not represent the concentration at any specific address. Manganese levels at your tap depend on local plumbing age and material, the condition of service lines in your immediate block, and the distance water travels from the nearest blending or storage point to your meter. CCR data answers the question of whether the utility is meeting regulatory thresholds across the system. It does not answer whether the water at your kitchen tap, bathroom fixture, or ice maker inlet is above or below the EPA advisory level. Point-of-use testing is the only way to know.

There are two practical paths to a verified result. The first is a California-certified laboratory test through a lab holding CA ELAP certification (California Environmental Laboratory Accreditation Program). A certified lab sends a sample collection kit, you collect a first-draw sample following the lab's instructions, and the result reports dissolved and particulate manganese separately. That separation matters for treatment selection: dissolved manganese must be oxidized before it can be filtered, while particulate manganese can be removed by filtration directly. A lab result gives you a defensible baseline that can be compared across years to track whether levels are changing.

The second option is an in-home screening by a licensed water treatment contractor, which provides a faster result useful for initial diagnosis. Screening tests are appropriate for deciding whether to order a full lab panel; they are not a substitute for certified lab analysis when sizing a permanent treatment system. Once you have test data, a contractor can match the treatment technology to the specific form and concentration of manganese present. For information about water filtration consultation and in-home water testing in the San Fernando Valley, see Noohi's water filtration services.

Health and Aesthetic Effects Above the SMCL

Above the EPA SMCL of 0.05 mg/L, manganese causes visible aesthetic effects. The most common are black and dark brown staining on fixtures, toilets, dishwashers, and laundry. Dissolved manganese oxidizes when it contacts air or chloramine residual in the distribution system, precipitating as manganese dioxide, which is responsible for the dark staining. At concentrations significantly above the advisory level, taste effects may also appear.

The California Health Notification Level of 0.5 mg/L is a public health notification trigger, not an enforceable MCL. However, long-term exposure at high manganese concentrations has been the subject of research. For current health guidance, consult the California State Water Resources Control Board and the EPA's secondary standards documentation, which reflects the agency's current assessment of aesthetic and health considerations at the advisory level. For homeowners concerned about manganese above the SMCL, point-of-use or whole-house treatment is the practical response, independent of what the utility is required to do.

How Water Filtration Addresses Manganese

Two main treatment approaches address manganese in residential water:

Reverse osmosis: NSF/ANSI 58-certified reverse osmosis systems that carry a manganese reduction claim reduce dissolved manganese at the point of use. Standard activated carbon filters do not reliably reduce manganese. An RO system is a point-of-use solution, typically installed under the kitchen sink, that addresses drinking and cooking water. It does not treat the water supply line feeding the whole house.

Whole-house oxidation-filtration: These systems oxidize dissolved manganese, converting it to a particulate form that can then be filtered out before it reaches fixtures and appliances. This approach addresses manganese at the supply line, protecting plumbing, dishwashers, washing machines, and water heaters from staining and deposit buildup. System sizing depends on the manganese concentration and flow rate. An in-home water test that distinguishes dissolved from particulate manganese is the right starting point before selecting a system.

Manganese also accumulates inside home appliances over time. In water heaters, manganese and iron particles settle to the bottom of the tank as sediment, reducing heating efficiency and shortening tank lifespan by accelerating corrosion of the anode rod and tank lining. In washing machines, manganese deposits on drum seals and inlet valve screens can discolor light-colored fabrics even when detergent is adequate and water temperature is correct. Because every fixture and appliance in the home shares the same supply line, whole-house oxidation-filtration treatment installed at the point of entry protects the full plumbing system. A point-of-use reverse osmosis filter at the kitchen tap does not protect the water heater, the washing machine, the dishwasher, or the showerheads in the rest of the house. Establishing which form of manganese is present, dissolved or particulate, determines whether oxidation is required before filtration or whether direct filtration at the supply line is sufficient.

For a side-by-side comparison of RO and whole-house filtration options using NSF certification data, see the detailed breakdown for SFV homes. If hard water is also present alongside manganese, the LADWP hard water guide for Woodland Hills covers softener and descaler options that address scale buildup separately from manganese staining.

Noohi Construction Inc. is a licensed general contractor providing water filtration system installation across Woodland Hills, Calabasas, Encino, Tarzana, and the broader San Fernando Valley. An in-home consultation establishes manganese levels at the tap before sizing any treatment system. Contact Noohi Construction to schedule a water quality assessment.

Sources used in this article: EPA Secondary Drinking Water Standards: Guidance for Nuisance Chemicals (40 CFR Part 143); LADWP 2024 Consumer Confidence Report; California State Water Resources Control Board; USGS National Water Information System (NWIS): California groundwater data.