Can Multi-family Homes Share a Grey Water System?

System Design Considerations

When designing a grey water system for multi-family homes, it’s essential to consider the number of users, water usage patterns, and the type of fixtures and appliances connected to the system. A general rule of thumb is to assume a minimum of 5 gallons per day per person for grey water generation. For a 4-unit multi-family home, this translates to 20 gallons per day. The system should be designed to handle the total grey water generation, including washbasins, showers, bathtubs, and washing machines.

Safety and Maintenance Requirements

To ensure the safe and efficient reuse of grey water, the system must be properly maintained, and regular checks are necessary to prevent contamination. The system should be equipped with a first flush device to remove the initial flow of dirty water from the grey water tank and a backflow prevention device to prevent contaminated water from entering the potable water supply. Regular water testing is also crucial to ensure the water quality meets the required standards.

Implementation Examples and Considerations

In some jurisdictions, grey water reuse systems are allowed in multi-family homes, but specific regulations and permits may be required. For example, in California, the California Plumbing Code allows grey water reuse systems in multi-family homes with a minimum of 3 units. The system should be designed and installed by a licensed plumber, and regular inspections and testing are necessary to ensure compliance with local regulations.