Land Use, Septic Systems & Water Wells

photo of tractor digging up water line

All homes must have a safe water supply and a system for proper disposal of sewage and wastewater. Some people in San Mateo County live in areas that do not have a community water supply or a municipal sewer system. If you live in one of these areas, you must install your own water and sewer systems.

The goal of the Land Use Program is to help people who live in these areas with these water supplies or sewage disposal systems. Inspection staff also certify septic system installers and percolation testers.

Revised OWTS Ordinance and Onsite Systems Manual

A revised Onsite Wastewater Treatment System (OWTS) Ordinance was approved by the County Board of Supervisors, and was effective on February 4, 2016. Our Onsite Systems Manual (OSM) is the implementation manual for the new OWTS Ordinance. The Ordinance and OSM are designed to comply with recent State OWTS Policy. The OSM was updated May 11, 2016, base on the first 4 months of use of the January version, using feedback from Environmental Health staff, consultants/designers, contractors, and planning and building department staff. Please ensure you are using the May 2016 version of the OSM.

Individual Sewage Disposal Systems

If you live in an area of San Mateo County that does not have a municipal sewer system, you must dispose of sewage and wastewater on your own property. In San Mateo County, the only approved system is a septic system. In a septic system, wastewater goes into a large underground tank. Pumping removes the solids in the tank. The liquid in the tank flows into the ground through a system of underground pipe and gravel. Over time, as the liquid soaks into the ground, organisms that live in the ground and in the sewage eat the organic materials and the harmful bacteria die.

Inspection staff will observe and approve the work when you need to install, repair, alter or destroy an individual sewage disposal system.

They do this by:

  • reviewing the proposed location for the system;
  • observing soil testing;
  • reviewing and approving plans;
  • observing the construction of the system;
  • verifying when a system has been destroyed safely; and
  • certifying installers and percolation testers.

When a septic system fails, sewage may back up into a home or it may pool onto the ground. Inspection staff investigate complaints of failed septic systems to make sure there is no hazard to public health.

Well Use in Droughts

If your well is not producing enough water for your needs, please review our list of frequently asked questions to ensure your family's water supply is safe.

Individual Water Supplies

Inspection staff regulate all domestic and agricultural water wells and springs. Before you move into your new residence or business, they will make sure that your water supply is safe. They do this by:

  • checking that all wells and springs are constructed properly;
  • certifying that the water output meets local requirements; and
  • monitoring and reviewing chemical and bacterial tests.


All people who install individual water supplies or sewage disposal systems must have a permit from Environmental Health.

Application approval can take some time. Inspection staff check permit applications to make sure that all installations will be safe for neighboring properties and surrounding areas. Often, community members and/or the County Board of Supervisors must approve the installation of new systems, as well.


Onsite Systems Manual

Complete Onsite Systems Manual 

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