This information was last updated on April 29, 2026. It will be updated on an ongoing basis as more information becomes available.

What happened to the water system in the Cuesta Park area?

The City replaces water main pipelines throughout Mountain View annually to maintain safe and reliable water service to customers. The City hired a contractor to replace a water pipeline along Bonita Avenue and other locations throughout the City.

Water main replacement typically involves installing new water main pipes and, once this is done, physically disconnecting the old pipeline from the operational water system. The old pipe is left in place and filled with a concrete slurry to fill the void of the “abandoned” pipe to provide it structure and prevent failure of the roadway.

At the Cuesta/Bonita intersection location, the new and old pipe were not disconnected, but were separated by a closed valve. On Friday, April 24, 2026, the contractor injected slurry into the old pipe. There was some seepage of the slurry through the closed valve between the old pipe and a live pipe carrying water to the residences.

Has the City experienced a similar situation?

No. The City follows all required best practices to maintain water safety during maintenance of and major improvements to the water system. The City also tests water quality on a regular basis and reports to the State as required. Occasionally, the City will discover and address bacterial contamination (such as coliform). The City has not encountered a situation such as this one, in which slurry was potentially in contact with drinking water. State contacts have indicated that this is also a unique experience for them

What did the City do when it found out what happened?

At 1 p.m. on Friday, April 24, as soon as the City became aware that the contractor had not fully disconnected the old water main at the Bonita/Cuesta location, City staff began sampling along the main line to determine the extent of the affected area and simultaneously shutting down the water main in the streets to prevent further spread of the contaminants. This also shut off water to the impacted homes.

Full shutoff between homes and the street main line was achieved by 2 p.m. The City flushed the main line with fresh water to draw out any contaminated water. City staff contacted the State Water Resources Control Board (State Water Board), which regulates water safety for water providers in California. The State Water Board issued a “Do Not Use” order and directed the City to conduct additional tests. At 7 p.m., City staff distributed a “Do Not Use” notice to all impacted households.

What area has been impacted by this incident? How many households does this include?

The streets that are affected by the temporary water shutoff are portions of Cuesta Drive, Leona Lane, Montalto Drive, Drucilla Drive, and Carla Court as shown in the map available at MountainView.gov/CuestaWaterMain. This includes approximately 67 households.

What is the status of the contractor’s work on the Water Main Replacement Project?

The City has issued a stop-work order for this contractor. The City will pursue all available remedies related to this incident. However, at this time, the immediate priority is restoring safe drinking water to affected residents.

How will the decision be made to restore drinking water access?

The State Water Resources Control Board provides direction on what types of tests the City must perform, and, based on the results, they provide additional direction (such as different types of tests and additional water main flushing). The process to restore full water access is one of ongoing communication between the City and the Water Resources Board and a series of iterative City actions. The State Water Board lifts the “Do Not Use” order when it is satisfied with the test results.

Is there any use of water that is currently allowed?

Yes, with the approval of the State Water Board, during the evening of Saturday, April 25, the City restored water flow into homes solely for the purpose of toilet flushing. And as of Wednesday, April 29, the City received guidance from the State Water Board that tap water can be used to water lawns and nonedible plants. The affected households are not to use tap water for drinking, cooking, handwashing, bathing, brushing teeth, washing dishes, or any other household use until further notice. City staff gave residents instructions on how to flush their water pipes and fixtures to work any potentially contaminated water through the household systems.

What is the City doing to restore access to drinking water in the Cuesta Park area?

The City is working around the clock to test the water at multiple locations in the affected area, flush the main water line, and flush the lines at household front yards (at the hose bibs). The purpose of this flushing is to force out any potentially contaminated water and draw good water into the system.

The City is expediting the testing process to the fullest extent possible. As noted in questions above and below, the testing process is complex and iterative. The City is in continual contact with the State Water Board regarding test results and next steps.

In addition to repeated rounds of flushing as noted above, the City is exploring options such as arranging for specialized water main cleaning services that will provide a higher velocity flushing and chlorination. The City is also performing visual inspections of water main segments. This requires construction activity to gain access to the water system and cameras to enable visual inspection. This construction activity may require temporary road closures. Residents will be provided with ongoing updates about such construction activity and road closures.

The City is coordinating with various water testing facilities and water service providers to bring all available resources to assist as quickly as possible. The City has declared a local state of emergency to facilitate requests to other agencies for “mutual aid,” expedite contracting processes for essential resources, and seek state and federal reimbursement for emergency-related City expenses.

How does water testing work? What are water tests looking for?

 The water testing process is complex (with different types of tests, result parameters, lab resources, and incubation periods). The testing process is also iterative. Each round of tests informs new directions from the State Water Board as to next steps. Following State direction, the initial tests were for organic contaminants, i.e. bacteria, such as coliform and E. coli. Tests for inorganic compounds such as metals (i.e. aluminum, lead, hexavalent chromium and others) are also underway. The testing protocol for this incident is being developed in real time since the possibility of contamination from slurry is a unique situation that neither the City nor the State have encountered before.

The basic testing process involves the following steps and timeframes:

1. The State Water Board directs which type of test is required (e.g. bacterial or various inorganic matter). Some tests are “binary,” providing either a “yes” or “no” as to the presence of the contaminant. Some tests are “enumerated,” providing a count regarding the presence of the contaminant. The range of acceptable contaminant levels differs depending on the test type.
2. City staff procures testing materials from the lab specific to the required test.
3. City staff collects samples at multiple locations.
4. Samples are delivered to a specially-equipped and certified lab for analysis.
5. The lab incubates the sample for the required timeframe, depending on the type of test. For example, the incubation for bacterial tests is 24 hours. The incubation period for inorganic materials can range from a few days to a few weeks.
6. The lab can often provide preliminary verbal results a bit in advance of delivery of the written report.
7. The State Water Board requires final, signed and certified reports to inform their decision about lifting the “Do Not Use” order.
8. Current State direction is that the City provide clear results from two back-to-back test samples, separated by 12 hours, before it will lift the order.

Why can’t water access be restored more quickly? How long will it take?

With each day’s complex and iterative testing and interaction with the State Water Board, the City receives additional information about the status of the water in the affected area and what actions and information the State Water Board requires before it can lift the “Do Not Use” order. Only the State Water Board can lift this order, and we do not currently know how long this will take. At this point, it is the City’s assumption that we will not have the clearance to restore drinking water access before Sunday, May 3. We are hopeful that the incident will not extend beyond this point. However, if it does, the City will continue to offer hotel accommodations and per diem payments for meals and incidental expenses. A QR code has been distributed to households to get information to support the per diem payments and identify any special needs. We will provide continual updates about the incident timeframe to affected residents as quickly and thoroughly as we can.

What have been the results of water testing so far?

 To date, the City has taken three rounds of samples for bacteria. Each round consists of two sets of samples, each taken from five locations within the affected area, with the two sets per round taken 12-hours apart (10 samples per round). Round 1 yielded positive results for bacteria at two locations. This was a “binary” test that only indicated a yes/no response for the presence of the bacteria. Round 2 bacterial tests were enumerated, which means that a numerical value was provided as to the amount of bacteria present. This round of tests yielded results of very low coliform counts at two locations. Staff is able to map and follow the migration of the bacteria based on test data and provide targeted effort to remove contaminants. Round 3 samples were delivered to the lab for analysis at 9 am on Wednesday, April 29.

At the State Water Board’s direction, the City is also testing for inorganic compounds such as metals (i.e. aluminum, lead, hexavalent chromium and others). The analysis times for such compounds are different from organic samples. The City is awaiting those results.

What are the health risks resulting from this incident

The City is working with the State Water Board to determine potential health impacts.

When and why do I need to flush the water pipes and fixtures in my home? How do I do this? What if I need help?

 The City instructed residents to flush in-home water lines and fixtures when access to water was restored on Saturday, April 25 solely for the purposes of toilet flushing. This flushing was necessary to clear potentially contaminated water from these lines and fixtures. The City provided instructions on how residents could conduct this flushing. These instructions are available at MountainView.gov/CuestaWaterMain. The City has procured plumbing services to assist residents who need help carrying out these instructions. Please let the City know if you need such assistance during any upcoming door-to-door visit, through the QR code form being distributed to residents, or by calling 650-903-6081 or emailing waterquality@mountainview.gov.
Once the City is able to lift the “Do Not Use” order clearing use for drinking and other household water uses, households will need to flush their internal pipes and fixtures again.

What resources are the City providing to residents impacted by this incident?

As described below, the City is actively coordinating around the clock across all City departments to provide a range of resources to households affected by this incident. These resources include drinking water; nondrinkable water for flushing toilets, watering plants, and other nondrinking household needs; plumbing services to assist with in home flushing of water lines and fixtures; hotel accommodations; reimbursement for meals and incidental expenses; access to City shower facilities; and enhanced police patrols.

• The City has been providing door-to-door check-ins by City Fire Fighters (three Fire Engines and 9 Fire personnel) twice a day since the first day of this incident. These ambassadors of the City are providing drinking water, buckets, water for non-drinking purposes, hand sanitizer, and important information updates and instructions. They are talking with residents to identify special needs, collect contact information, and answer questions to the fullest extent possible.
  
  
• The City has established a contract with Water World to provide a drinking water delivery service to households in the affected area, with service beginning on April 30.
  
  Beginning April 30, the Fire Department will scale back direct water deliveries and will provide service on a case-by-case basis. Residents needing assistance may contact the City at 650-903-6081 or waterquality@mountainview.gov.
  
  
• The City has procured plumbing services to assist residents who need help carrying out the instructions for flushing in-home water lines and fixtures. Please let the City know if you need such assistance during any upcoming door-to-door visit, through the QR code form being distributed to residents, or by calling (650)903-6081 or emailing waterquality@mountainview.gov.
  
  
• The City has coordinated with several local hotels to provide rooms for affected households and continues to identify additional hotel options, with a focus on securing rooms with kitchen facilities where possible. The cost of rooms secured under a City agreement is billed directly to the City. Alternatively, residents may arrange their own hotel or short-term rental accommodations and will be reimbursed up to the Federal lodging rate of $192 plus tax per night.
  
  
• The City is providing a per diem reimbursement for meals and incidental expenses, such as laundry, at the Federal rate of up to $92 per day per household member. Data collection is currently underway to gather the information needed to begin processing payments to impacted residents, including through a QR code that residents can use to submit their information.
  
  
• The City has provided access to showers at the City’s two pool facilities (Rengstorff Park Aquatics Center and Eagle Park Pool). The City is working to provide access to showers at additional facilities.
  
  
• The City is evaluating options to provide a credit on household water bills to account for water used by the City to flush residential water lines at the exterior yard bibs.
  
  
•  City staff continue to identify and respond to emerging household needs. Residents can email waterquality@mountainview.gov or call 650-903-6081 to communicate their needs. In addition, the City will hold a neighborhood meeting on Friday, May 1 to provide updates to and be in conversation with residents.
  
  
• The Police Department is conducting regular patrols of the incident area to maintain safety and identify any potential security concerns. In addition, the City is monitoring any reported incidents of phishing that seek to take advantage of the current water system incident. If you have experienced or are experiencing a safety incident or concern, call 9-1-1 for emergencies and (650) 903-6344 for non-emergency matters.

Can the City provide drinking water in larger than single-use containers?

Yes. The City has established a contract with Water World to provide a drinking water delivery service to households in the affected area, with service beginning on Thursday, April 30. Water World representatives will be available during this delivery period to share information about their services.

Each household is eligible to receive an initial delivery of three 5-gallon water containers and a hand pump, with replacement containers delivered daily. The City is aware that some residents are staying in hotels or are out of town and may not currently need water delivery. Water World will leave water at households at which they are able to connect with a resident or at households where residents have contacted Water World directly (at the number below) with special delivery instructions. This will help avoid having visible, untended deliveries at a residence for an extended period of time.

Water and pumps that Water World is not able to deliver on April 30 will be stored at Mountain View Fire Station 2, located at 160 Cuesta Drive. Residents who are not home and who did not leave Water World special delivery instructions can pick up their water and pump at Fire Station 2 at a time convenient to them. Please note, the fire company may not be available in the Station if they are on a fire or emergency medical call somewhere in the city.

Water World: (408)641-5440
Mountain View Fire Station 2, 160 Cuesta Drive, (650)903-6340

This delivery of larger water containers will better meet household needs for such uses as dish washing and will reduce the environmental impact of single-use water bottles.

I have more recyclables than can fit into my cart. What can I do?

The City is aware that recycling bins may not be big enough to accommodate all the water bottles being used during this time. Residents can put out extra bags next to their recycling bins on their normal pick-up day. While paper bags, cardboard boxes, or reusable bins are preferred, plastic bags can be used as long as there is a note on them that says “recycle.” Residents can also drop off their plastic bottles at the Mountain View Recycling Center, 935 Terra Bella Ave.

What do I do if I need to stay in a hotel?

The City is currently providing hotel accommodations through Sunday night, May 3 (with checkout on Monday, May 4). The City has coordinated with several local hotels to provide rooms for affected households and continues to identify additional hotel options, with a focus on securing rooms with kitchen facilities, where possible. The cost for rooms secured under a City agreements is billed directly to the City. Any mandatory pet fees or parking fees will also be covered by the City. Visit MountainView.gov/CuestaWaterMain for a list of participating hotels (subject to room availability).

Residents may also arrange their own hotel or short-term rental accommodations and will be reimbursed up to the Federal lodging rate of $192 plus tax per night.

For assistance with hotel accommodations, please call (650)903-6081 and press 2.

What if I select a hotel or home rental that isn’t being provided directly by the City?

 Residents may also arrange their own hotel or short-term rental accommodations and will be reimbursed up to the Federal lodging rate of $192 plus tax per night. Paid hotel invoices will be required for reimbursement. For assistance with hotel accommodations, please call (650)903-6081 and press 2.

If I want to want to stay in my home, where can I shower?

The City has provided access to showers at the City’s two pool facilities (Rengstorff Park Aquatics Center and Eagle Park Pool). See MountainView.gov/CuestaWaterMain for current shower hours by day and location. The City is working to provide access to showers at additional facilities.

Is there any reimbursement for meals and incidental expenses?

Yes. The City is providing a per diem reimbursement for meal and incidental expenses, such as laundry, at the Federal rate of up to $92 per day per household member. The City has distributed a QR code for residents to complete a form that will collect the information needed to calculate payments and to issue reimbursement checks in accordance with the Federal rate. The City does not believe these reimbursements are subject to tax and no Form 1099 will be issued. However, residents should consult their tax advisor regarding their individual circumstances.

The City is currently preparing to issue reimbursement checks on Friday, May 8, for the period from the start of the incident on Friday, April 24, through Sunday, May 3. The City hopes the incident will be resolved by that time. If the City receives guidance from the State Water Board indicating that additional testing or steps are required and the “Do Not Use” order cannot be lifted by Sunday, May 3, reimbursement will be extended for additional days as needed. The City will continue to update affected residents regarding the duration of the incident and the reimbursement process for meal and incidental expenses.

Will I be responsible for any increase in water costs associated with the City’s flushing of the main to my house?

The City is evaluating options to provide a credit on household water bills to account for water used by the City to flush residential water lines at the exterior front yards. Note that the cycle/time period for the water bill you are slated to receive in the next week ended before the start of this pipeline incident.

How is the City working to keep the neighborhood safe during this incident?

The Police Department is conducting regular patrols of the incident area to maintain safety and identify any potential security concerns. If you have experienced or are experiencing a safety incident or concern, call 9-1-1 for emergencies and (650)903-6344 for non-emergency matters.

The City is also monitoring reports of any potential phishing attempts seeking to take advantage of the current water system incident. On Wednesday, April 29, a Los Altos resident notified the City about an attempted phishing scam likely related to the current incident.

Please be advised that the City will not call, text, or email individuals who are not located within the affected area. If you receive these types of phishing scams, please check out the tips below to help prevent becoming a victim.

• Do not click suspicious links — If it looks questionable, don’t click it.
• Verify the sender — Verify email addresses and phone numbers carefully.
• Beware of red flags — Urgent requests, threats, or too-good-to-be-true offers.
• Do not share personal info — Legitimate organizations won’t ask for personal sensitive details via email or text.

Has the City declared a local state of emergency and what does this mean?

Yes. The City declared a local state of emergency on Saturday, April 25, which was ratified by the City Council on Tuesday, April 28. Having this declaration in place facilitates requests to other agencies for “mutual aid,” expedite contracting processes for essential resources, and allows the City to seek state and federal reimbursement for emergency-related City expenses.

How do I stay informed about the status of water restoration and available resources?

There are a number of ways for residents to get the latest information about water restoration and available resources. The City provides online updates once or twice per day which are posted on the City’s website, shared on social media, and sent to residents via the contact information provided to the City. (Visit MountainView.gov/CuestaWaterMain.) The City is also developing a specific and more comprehensive web section for this incident. On a regular basis, The City produces handouts, which are delivered during door-to-door check-ins. City staff can also check in periodically at the hotels under agreement with the City. The City provides interviews and responses to media inquiries to support timely, accurate reporting to the general public. The City is planning a neighborhood meeting for Friday, May 1.

What do I do if I have questions?

 For the most updated information, visit MountainView.gov/CuestaWaterMain. If you have any questions about the incident itself, please call 650-903-6081 and press 1.