Water Main Installation Process

The San Francisco Public Utilities Commission owns and operates more than 1,200 miles of water pipelines in San Francisco. These water pipelines, also called water mains, deliver high quality drinking water to your tap. Approximately 20% of San Francisco’s water mains are about 100 years old and need to be replaced. 

We replace aging and vulnerable water mains each year. The process of replacing aging water mains involves many steps. Construction will not happen all at once. Crews will need to return to the same block several times to work, often with months between visits. 

Water main replacement includes the following steps:

1. Locate Underground Utilities (called Potholing) 
   Crews dig small holes in the street along the pipeline alignment to confirm the location of the underground utilities, such as cable, gas, fiber, and wastewater lines.

2. ---

   Mobilization
   Crews bring equipment and supplies and store them at a pre-approved location on the street or another nearby location where they will be needed.  

3. ---

   Water Main Installation 
   Crews sawcut and remove the asphalt and concrete from the area where the new water main will be placed. They dig a trench down to the depth of the new water main. The new water pipe is lowered into the ground, one pipe section at a time. These pipeline sections are connected together in the trench and this process continues until they reach a point where they can be connected to the existing water main network.     

4. ---

   Backfill Trench and Temporary Street Restoration
   Crews will carefully place sand backfill material into the trench. Temporary asphalt will be placed on top of the trench so people can drive over it.  
   
   Final restoration of the asphalt in the street will happen later in the project.  

5. ---

   Testing the New Water Main 
   Once the new water main segment has been put into the trench, crews will test the line to ensure there are no leaks. They do this by putting water at higher pressures in the new pipeline segment for a period of time. If no leaks appear, the pipe passes. 

6. ---

   Connection to Existing Water Main
   Once the new pipeline passes the leak test, crews will connect it to the existing water main on the street, ensuring a water source for disinfecting the new pipe. During this process, the newly installed pipeline remains isolated from the distribution system that serves customers.
   
   Water service to a property would be temporarily impacted during this time. 

7. ---

   Disinfection 
   At this stage, the team flushes the water main and injects chlorine inside the pipe to ensure thorough disinfection of the pipe interior. Crews then flush the main again and test the water quality in the mains. Once water quality passes, the main is ready to serve customers. 

8. ---

   Connection to Customers 
   San Francisco Water Division crews construct new service lines from the new water main to customer’s properties. This enables customers to receive water from the new water main.  
   
   Water service to a property would be temporarily impacted during this time.  

9. ---

   Remaining Connections to New or Existing Water Main 
   Crews continue to dig and construct new connections between the new water main and the existing water main delivering water to the area. 
   
   Water service to a property would be temporarily impacted during this time. 

10. ---

    Backfill Trench and Temporary Street Restoration as Connections are Finished and Tested 
    Crews will carefully place sand backfill material into the trenched areas where the new pipeline connections have been made. Temporary asphalt is placed on top of the trench so people can drive over it.  
    
    Final restoration of the asphalt in the street will happen later in the project. 

11. ---

    Repeat in different segments all along the project area 

12. ---

    Final Paving Restoration
    When the entire project is complete, oftentimes months after the work on any particular block is completed, crews will perform final pavement restoration in the project area.