RANCHO MURIETA, CA (MPG) - Just two days after Rancho Murieta Community Services District staff told directors that manganese levels in the community’s drinking water were within state guidelines, the district issued a precautionary alert advising residents to give infants and babies bottled water because manganese had reached what it described as “EPA maximum contaminant levels.”

The June 19 alert, distributed through the district’s new SiRcom Smart Alert notification system, stated: “Precautionary Alert: Manganese Levels are at EPA’s maximum contaminant levels. Infants and Babies should be given bottled water until further notice.”

Less than 13 hours later, at 8:24 a.m. Saturday, the district notified residents that the advisory had been lifted: “Update for Rancho Murieta residents. Manganese levels have returned to normal levels. Water is now ok for consumption.”

The rapid reversal has raised questions about what caused the spike, how high manganese levels reached, whether the issue originated at the water treatment plant and what actions district staff took to restore water quality.

A notice later posted on the district website advised residents that it was safe to resume normal water use and promised a detailed explanation on Monday. 

“We plan to post a report with details on what happened Monday,” the website stated.

Residents experiencing brown water were advised to flush household lines for 10 minutes and contact the district if the problem persisted.

Because the River Valley Times was going to press on Monday, June 22, questions were emailed to district officials on Sunday, June 21, seeking details about the incident. A response was not received before publication.

Among the questions posed were what manganese level triggered the advisory, where the sample was collected, whether the result came from laboratory testing or in-house monitoring, what caused the apparent spike, and what test result allowed the district to lift the warning less than a day later.

The district has indicated that additional information will be released on Monday, June 22. Once that information becomes available, the River Valley Times will post an updated story online at rivervalleytimes.com.

The advisory came shortly after Interim Director of Operations Travis Bohannon discussed new state manganese reporting requirements during the June 17 board meeting.

Bohannon told directors that the State Water Resources Control Board had recently issued new manganese reporting requirements that took effect June 1. He said the district already conducts manganese testing monthly, exceeding the state’s quarterly reporting requirement, and indicated the district’s treated water remained within applicable guidelines.

Bohannon explained that manganese occurs naturally in Rancho Murieta’s reservoirs during the summer.

Manganese is a naturally occurring mineral commonly found in both surface water and groundwater. According to the California State Water Resources Control Board, manganese is an essential nutrient, but elevated concentrations can pose health concerns, particularly for formula-fed infants and young children, who absorb and retain manganese more readily than adults.

On June 2, the state’s Division of Drinking Water revised health-based notification and response levels for manganese after reviewing scientific studies that found potential developmental and neurological impacts from prolonged exposure to elevated manganese levels, especially in formula-fed infants.

State officials describe manganese as both an aesthetic and a health issue. At lower concentrations, it can cause discolored water, staining of plumbing fixtures and laundry, and sediment buildup. At higher concentrations, prolonged exposure may pose health risks to sensitive populations.

The district has not yet disclosed the manganese concentration that triggered the June 19 advisory, making it impossible to determine whether the exceedance involved California’s secondary drinking water standard, a health-based notification level or another threshold.

Manganese has been a recurring issue for Rancho Murieta’s water system.

In 2019, the district experienced a significant yellow-water event that generated approximately 80 customer complaints. District documents from that period identified dissolved manganese as the cause of the discoloration.

At the time, district officials reported that Water Treatment Plant No. 2 was successfully removing manganese from the water supply, while Water Treatment Plant No. 1 was temporarily taken offline because it was unable to reduce manganese concentrations to acceptable levels. 

District reports indicated that manganese levels tend to increase during warmer weather, requiring treatment adjustments and additional monitoring.

The district eventually resolved the 2019 incident through operational changes, treatment modifications and extensive flushing of the water distribution system.

For now, residents know only that manganese levels rose high enough Friday evening to prompt a bottled-water recommendation for infants and babies and that subsequent testing allowed the district to lift the advisory Saturday morning.

What remains unclear is whether the elevated manganese level was detected in raw water, treated water or the distribution system; whether the result represented a short-term spike or a broader treatment issue; and whether the recently revised state manganese notification requirements played any role in triggering the advisory.

The district has promised a detailed explanation on Monday, June 22. Until then, many of the key questions surrounding the brief advisory remain unanswered.