Skip to main content Skip to site navigation

Using Rain, Gray and Other Alternative Water Sources

General information

As California continues to experience one of the most severe droughts in its history, many residents and businesses are looking for innovative ways to conserve and reduce consumption of drinking water.

There are a number of simple, low-cost methods that can be used to conserve water. These include:

  • Limiting showers to five minutes or less
  • Capturing water in a bucket while washing produce or waiting for your shower water to heat up and then using that water for irrigating or for flushing your toilets
  • Upgrading appliances and fixtures to energy- and water-efficient models
  • Repairing any leaking faucets and running toilets
  • Replacing lawns with drought-tolerant landscaping or xeriscaping
  • Learning about your daily water use (available on your water bill or use the Alliance for Water Efficiency’s Water Use Calculator

We encourage you to check with your water provider for incentives to conserve water.

One way to save water is by capturing and using alternative water sources, such as rainwater and gray water, to use for non-drinking water purposes like landscaping. We encourage safe use of several alternative water sources. This website is to help guide water customers at both the residential and commercial scale in determining the requirements for having an onsite alternative water system.

Not sure whether your project needs Environmental Health review? Fill out this form.

Alternative Water Sources

There are several types of alternative water sources that can be generated onsite for non-drinking uses. These sources include:

  • Rainwater: collected from roof surfaces or other approved, above-ground collection surfaces.
  • Stormwater: collected at or below ground through approved collection surfaces. This type of non-potable water source is typically dirtier than rainwater and may contain contaminants like oil, grease and volatile organic compounds (VOCs).
  • Foundation drainage: nuisance groundwater that is extracted to maintain the structural integrity of a building.
  • Irrigation well: groundwater from a permitted well that has not been certified as a potable water source.
  • Gray water: wastewater from bathtubs, showers, bathroom sinks, clothes washing machines, and laundry tubs. It does not include wastewater from toilets, utility sinks, kitchen sinks, or dishwashers. Learn more about how to safely use gray water here.

San Mateo County Health System does not allow blackwater(even if treated) for residential or commercial use because of public health concerns and because it requires advanced water treatment methods and higher, more costly water quality monitoring

Approved Uses of Alternative Water

How and where non-potable water sources can be used depends on several factors. These factors include:

  • Potential for human contact: non-drinking water sources may contain viruses, bacteria and chemicals that can be harmful to humans and animals.
  • Scope: whether the onsite water reuse system being proposed is for residential or commercial use. Multi-unit residential (4 or more units) is considered commercial.
  • Scale:whether the proposed onsite water reuse system designed appropriately to ensure alternative water sources do not pond or run-off and cause environmental and public health issues.
  • Treatment: depending on the alternative water source proposed and the potential for human contact, treatment and/or disinfection may be required.

Residential Onsite Water Reuse

All onsite water reuse systems may require a permit from your local building department.

When plan review from Environmental Health is NOT required:

  • A gray water system comprised solely of a clothes washer system that diverts gray water to sub-surface irrigation or an appropriately configured and maintained mulch pile does not need to submit plans to or require a permit from Environmental Health. This is often referred to as Laundry to Landscape. These types of systems must meet all requirements specified in Section 1602.1.1 of the Uniform Plumbing Code. San Francisco Public Utilities Commission has a thorough Gray Water Design Manual.
  • Similarly, standalone rainwater barrels that are not connected to the home’s internal plumbing supply do not require plan submission or a permit from Environmental Health.

When plan review from Environmental Health is required:

In addition to building department permits, plan submission to the Environmental Health Division is required for any residential project proposing to use:

  • treated rain, gray, or foundation drainage water used for surface drip and/or spray irrigation
  • treated rain or well water for non-drinking applications inside the home such as toilet flushing and clothes-washing
  • untreated gray water used for subsurface distribution (if scope is beyond simple clothes-washer/Laundry to Landscape diversion)

Other requirements

  • All equipment including treatment components must meet NSF/ANSI Standard 350.
  • Alternative sources should not intermingle and must be separate water treatment and/or delivery systems.
  • You may be required to install backflow protection at each water service meter serving your residence. Please contact your water provider for more information or visit the San Mateo County Cross Connection Control Program web page.

Commercial Onsite Water Reuse

In addition to tertiary treated recycled water, Environmental Health may allow commercial properties to use onsite alternative water sources described above for internal and external non-potable water applications. The use of onsite treated blackwater is currently prohibited. All commercial projects proposing use of recycled or alternative water sources must submit plans to Environmental Health for approval before installation and use. Projects will be evaluated on a case-by-case basis.

How to Submit Plans to Environmental Health

Applicants wanting to install an onsite water system must submit an Environmental Health Review Application (and three sets of plans if required). The application fee for the plan review may be required. Additional fees and/or information may be required depending on the complexity of the project. This is in addition to any potential building department permits. Please contact Environmental Health at (650) 372-6200 for an application. We will try to have the application available on this site soon!

Treated Water Quality Requirements

Environmental Health will determine minimum water quality and monitoring requirements based on the type of non-potable water source, treatment, and intended uses proposed for the project.

Materials & Links

Commands