Pipes in an area of Mountain View affected by last week’s water main breach will undergo a “super chlorination” treatment after water in them has consistently tested positive for coliform bacteria, the city said Sunday night.  

On Monday, water lines on Drucilla Drive and Carla Court will be injected with a high concentration of chlorine — specifically, lines affecting 23 households on Drucilla Drive between Leona Lane and Montalto Drive and all of Carla Court, the city said.  

The process will involve setting up temporary water lines so that each house has access to water during the chlorination period. These lines will work through a temporary connection from a hydrant to above-ground lines, according to the city. Water will be shut off briefly during the changeover and each household will be notified when the time comes.  

For the project, a hole will be dug at each end of Drucilla Drive, at Leona Lane and Montalto Drive, to disconnect the water pipe and isolate it. The chlorine will then be injected into the closed section of pipe and it will stay there for 24 hours. From there it will be flushed out and two rounds of water samples will be taken 12 hours apart to check for bacteria.  

During all of this, the boil order will remain in effect. On Sunday, the city told residents they will have to boil their tap water at least through next weekend.   

City crews have been working to rectify the water problem after About 67 households in the 600 block of Cuesta Drive and 600-700 block of Leona Lane had water shut off due to a breach of a water main during maintenance work ten days ago, according to Lenka Wright, a City of Mountain View spokesperson.  

Wright said that the water shutoff was due to cement slurry getting into the system.  

On Friday, households received the updated notice to boil water from the tap for drinking and cooking. It was a step up from a previous advisory: “Unsafe Water Alert – Do Not Use Your Water,” which left residents only able to use water to flush toilets.   

Water from the tap must be boiled for at least one minute if it is to be used for drinking or cooking, or to prepare drinks such as coffee, tea or beverage mixes. Boiled water must be used to wash any produce or food prep areas, to make ice, and to brush teeth.  

A water main break in Mountain View, Calif., on Friday, April 24, 2026, disrupted service in the Cuesta Park neighborhood. Residents in at least 67 households are now under a boil-water order after contamination was detected in parts of the system, city officials said.
(City of Mountain View via Bay City News)

Tap water is now okay to use for baths or showers, to wash hands, to do laundry or to run the dishwasher, the city said. 

The Mountain View City Council declared a state of emergency on April 25, which will allow the city to seek reimbursement from the state and the federal government for expenses related to the incident.   

Note to readers: This story has been updated 11:48 p.m. with more details about water testing and planned “super chlorination” of affected pipes.

Katy St. Clair got her start in journalism by working in the classifieds department at the East Bay Express during the height of alt weeklies, then sweet talked her way into becoming staff writer, submissions editor, and music editor. She has been a columnist in the East Bay Express, SF Weekly, and the San Francisco Examiner. Starting in 2015, she begrudgingly scaled the inverted pyramid at dailies such as the Vallejo Times-Herald, The Vacaville Reporter, and the Daily Republic. She has her own independent news site and blog that covers the delightfully dysfunctional town of Vallejo, California, where she also collaborates with the investigative team at Open Vallejo. A passionate advocate for people with developmental disabilities, she serves on both the Board of the Arc of Solano and the Arc of California. She lives in Vallejo.