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# 1503.8 Procedure for Estimating Gray Water Discharge

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Gray water systems shall be designed to distribute the total amount of estimated gray water on a daily basis. The water discharge for gray water systems shall be determined in accordance with Section 1503.8.1 or Section 1503.8.2.

**Exception:**

*It is not the intent of this section to require that all gray water must be handled by an irrigation field or disposal field. It is acceptable for excess gray water to be diverted to the building sewer through a diverter valve or overflow drain as permitted in this chapter.*

The gray water discharge for

*residential occupancies*shall be calculated by water use records, calculations of local daily per person interior water use, or the following procedure:(1) The number of occupants of each dwelling unit shall be calculated as follows: | |

First Bedroom |
2 occupants |

Each additional bedroom |
1 occupant |

(2) The estimated gray water flows of each occupant shall be calculated as follows: | |

Showers, bathtubs, and lavatories |
25 gallons (95 L) per day/occupant |

Laundry |
15 gallons (57 L) per day/occupant |

(3) The total number of occupants shall be multiplied by the applicable estimated gray water discharge as provided above and the type of fixtures connected to the gray water system. |

The

*Authority Having Jurisdiction may utilize the gray water discharge procedures listed below,*water use records or other documentation to estimate gray water discharge.
Daily discharge from lavatories may be determined by the following equation:

Where:

The number of occupants = square footage of the building divided by the occupant load factor from the California Plumbing Code Chapter 4, Table A.

Lavatory fixture flow rate, new construction = That from the California Green Building Standards (CALGreen) Code Section 5.303.2.3

Lavatory fixture flow rate, existing fixtures= Actual flow rate for existing fixtures

3 = Average number of uses per person per day

Occupants X lavatory flow rate X 3

**(Equation 15.1)**Where:

The number of occupants = square footage of the building divided by the occupant load factor from the California Plumbing Code Chapter 4, Table A.

Lavatory fixture flow rate, new construction = That from the California Green Building Standards (CALGreen) Code Section 5.303.2.3

Lavatory fixture flow rate, existing fixtures= Actual flow rate for existing fixtures

3 = Average number of uses per person per day

Daily gray water discharge from showers may be determined by the following equation:

Number of daily uses X shower flow rate X 5 minutes

**(Equation 15.2)**
Daily gray water discharge from commercial clothes washers may be determined by the following equation:

Where:

Water Factor= Gallons per cubic foot

6 = Average number of uses per day

Cubic feet of capacity X Water Factor X 6

**(Equation 15.3)**Where:

Water Factor= Gallons per cubic foot

6 = Average number of uses per day

**Note:**Cubic feet of capacity and Water Factor are contained in product specifications or are available from the washer manufacturer.
Gray water systems using tanks shall be designed to minimize the amount of time gray water is held in the tank and shall be sized to distribute the total amount of estimated gray water on a daily basis.

**Exception:**Approved on-site treated nonpotable gray water systems.

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