The design, installation, and maintenance of a graywater system are very important. Here you will find best practices, installation tips, and information on what to do in case your graywater system is not performing at 100%.


Questions Homeowners Need to Answer

To design your graywater plumbing system you should know:

  • How much water is needed for your garden?
  • How much water will be produced from your graywater systems?
  • What type of water do the plants need (rainwater is acidic, graywater is basic)?
  • When do you need it (daily, monthly, bi-annually)?
  • Where are you going to get it from (shower, sink, laundry machine)?
  • How are you going to deliver the water to the garden (pump system, gravity flow)?
  • Which distribution system do you plan to use (sub-surface or mulch basin)?


Clothes Washer Graywater System

Two rough drawings depicting the second sandpipe method and the three way valve method for clothes washer graywater systems.


Design and Installation

Attach the washing machine discharge hose to either a 3-way valve or to a second standpipe. Clothes washer discharge water must be capable of being diverted to the landscape or to the sewer. The 3-way valve provides an easy way to switch between the two. The 3-way valve or the two clothes washer standpipes shall be labeled to clearly identify the position to discharge to the sewer and to the graywater system. Once outside the building, the graywater must drain directly to the irrigation system. Piping shall be permanently labeled at 5-foot increments with: “CAUTION: NONPOTABLE WATER, DO NOT DRINK.” Graywater must not be sprayed or discharged on the surface of the ground. A mulch basin with 2-inch cover is the simplest system allowed for distribution and irrigation with graywater. All graywater must be used the same day it is produced.


16 Requirements of a Clothes Washer Graywater System 

  1. The design shall allow for the user to have the option to direct the flow to the irrigation/disposal field or the building sewer. The direction control of the graywater shall be clearly labeled and readily accessible to the user.
  2. The installation, change, alteration or repair of the system shall not include a potable water connection, tank or a pump and shall not affect other building, plumbing, electrical or mechanical components including structural features, egress, fire-life safety, sanitation, potable water supply piping or accessibility.
  3. The graywater shall be contained on the site where it is generated.
  4. Graywater shall be directed to and contained within a subsurface irrigation or disposal field.
  5. Ponding or runoff is prohibited and shall be considered a nuisance.
  6. Graywater shall be released no less than two (2) inches below the surface of mulch, rock, or soil.
  7. Graywater systems shall be designed to allow no contact of the graywater with humans and domestic pets.
  8. Water used to wash diapers or similarly soiled or infectious garments shall not be used and shall be diverted to the building sewer.
  9. Graywater shall not contain hazardous chemicals derived from activities such as cleaning car parts, washing greasy or oily rags, or disposing of waste solutions from home photo labs or similar hobbyist or home occupational activities. Graywater shall not contain waste from kitchen sinks or dishwashers.
  10. Exemption from permit requirements of this code shall not be deemed to grant authorization for any graywater system to be installed in a manner that violates other provisions of this code or any other laws or ordinances of the Enforcing Agency.
  11. An operation and maintenance manual for a graywater installation shall be provided. The manual is to remain with the building throughout the life of the system and indicate that upon change of ownership or occupancy, the new owner or tenant shall be notified the structure contains a graywater system.
  12. Comply with all other aspects of Chapter 16A, part 1 of the 2007 California Plumbing Code (e.g. distance from property line, distance from building structure, etc).
  13. Exemption from permit requirements of this code for clothes washer graywater systems shall not be deemed to grant authorization to perform other work that requires a permit.
  14. Any required fire rated separation, such as the one between the house and the attached parking garage, shall be maintained.
  15. The irrigation/disposal field shall not be located on any slope steeper than 3:1 (horizontal:vertical).
  16. Any alteration to the building or plumbing, electrical, or mechanical system requires a permit.


Simple & Complex Graywater Systems


Illustration depicting toilet, sink and bathtub water flowing to irrigation system.


Design and Installation

This system shows graywater being diverted from the sink and bathtub to a row of plants via an irrigation system. Toilet water cannot be used for graywater and must exit the house through the main sewer line. This system also shows a surge tank for temporarily holding back large drain flows (for 24 hours or less), a 3-way valve to switch between the graywater system and the sewer system, and a vent to allow for air circulation. An above ground tank has to be water tight and protected from corrosion.


Treated Graywater System

Currently, the City of Los Angeles does not allow the use of graywater treatment systems for expanded uses of graywater such as for surface irrigation or toilet flushing due to lack of approved standards. This information will be updated once standards are adopted for graywater treatment systems.

Typical Layout for a Graywater System


Illustration depicting a single family home with pipe system within property, and a cross section of graded soil, gravel and buried water pipe.

2010 California Plumbing Code, Appendix G, Figure G-5 Gray Water System Typical Irrigation Layout

Design and Installation

Graywater lines have to be 5 feet away from a domestic water service line and 10 feet away from the public water main since it is not water tight. Disposal fields must be 5 feet from property lines and buildings, and 100 feet from streams. Piping to disposal field shall be solid pipe sloping ¼ per foot to the point of connection to the leach field. Minimum 3-inch perforated pipe is required for disposal fields. Perforated pipe shall be installed level. Filter material and aggregates from ¾- to 2½-inches shall be placed in the trench. Aggregate can be clean stone, gravel, slag or similar materials. Leach lines can be up to 100-feet long and spaced as close as 4 feet apart.

Graywater Tanks & Pumps

Graywater systems using tanks shall be designed to minimize the amount of time graywater is held in the tank. Water must be discharged within 24 hours after entering the tank. Graywater systems shall be sized to distribute the total amount of estimated graywater on a daily basis. A 50 gallon storage tank is usually sufficient. If a tank or pump is installed, a plumbing permit will be required from LADBS.


Typical Graywater System with an Underground Tank and Pump (Permit Required)

Illustration depicting a below ground tank and pump Graywater system


Typical Graywater System with an Above Grade Tank and Pump (Permit Required) 

Illustration depicting an Above Grade Pump and Tank Graywater System


Typical Graywater System with Tank (Permit Required)

Illustration Depicting a Graywater System with a Single Tank

Typical Graywater System with Multiple Tanks (Permit Required) 

Illustration Depicting a Graywater System with Multiple Tanks

Rules for Tank Construction

  1. When system design includes a tank, specifications for the tank shall be submitted to the Enforcing Agency for approval. Such plans shall show all dimensions and other pertinent data.
  2. Tanks shall be constructed of solid, durable materials not subject to excessive corrosion or decay and shall be water-tight.
  3. Each tank shall be vented as required by Chapter 9 of this code, shall be sealed against vermin and mosquitoes, and have an access opening to allow for inspection and cleaning.
  4. Each tank shall have its rated capacity permanently marked on the unit. In addition, a sign stating "GRAYWATER IRRIGATION SYSTEM, CAUTION — UNSAFE WATER" shall be permanently marked on the holding tank.
  5. Each tank shall have an overflow drain. The overflow drain shall have a permanent connection to the building drain or building sewer, upstream of septic tanks, if any. The overflow drain shall not be equipped with a shutoff valve.
  6. The overflow drain shall not be less in size than the inlet pipe. The vent size shall be determined based on the total graywater fixture units as outlined in Table 7-5 of this code. Unions or equally effective fittings shall be provided for all piping connected to the holding tank.
  7. Each tank shall be structurally designed to withstand all anticipated earth or other loads. Tank covers shall be capable of supporting an earth load of not less than three hundred (300) pounds per square foot (1,464.7 kg/m2) when the tank is used for underground installation.
  8. The overflow system must be designed so that the tank overflow will gravity drain to the existing sewer line or septic tank. The tank shall be protected against sewer line backflow by a backwater valve.
  9. An overflow drain and backwater valve is not required on a clothes washer system.


Cross Connection Control

(LADWP Rule 16-D)

Where graywater systems are installed and a potential for cross connection with the potable water supply exists, a reduced pressure principle backflow prevention device (RPBP) is required on the water service. The cross connection control device is required to be installed downstream of the water meter and prior to any branches off the water service.

Additional cross connection control devices may be required by the Los Angeles Department of Building and Safety or the Los Angeles County Department of Public Health in accordance with the Los Angeles Plumbing Code and other codes to protect the potable water supplied within the building.


Graywater Diversion Devices Component Maintenance Required Frequency

Clean Filter

- filter should be removed and cleaned, removing physical contaminants (Sand, lint, hair, etc.)

Replace filter As recommended by manufacturer or as required (usualy every 6-12 months)
Surge Tanks Clean out sludge from surge tank Every six months
Sub-surface Irrigation Distribution System

Check that water is dispersing

- regularly monitor soil to ensure all areas are wet after an irrigation period

Soil Condition

Check soil condition.

Signs of soil problems include:

- damp ground hours after irrigation

- surface ponding and run-off of irrigated water

- poor vegetation growth

- unusual odors

- clumping of soil

-fine sheet of clay covering surface


State of New South Wales and the Department of Energy, Utilities and Sustainability (Australia)