Flowing Forward: Basics in Graywater Recycling and Water Conservation

With climate patterns changing and becoming more unpredictable, water conservation measures are becoming critical to reduce water consumption in our buildings. One way to reduce water consumption and decrease your water utility bill is to utilize a graywater recycling system. Below, we will explore graywater and graywater recycling systems, where they are best to be implemented, and what the requirements are around these systems.

What is Graywater?

Let’s start with the basics. What is graywater? Graywater is nonpotable wastewater from washing machines, showers, bathtubs, lavatories, and HVAC Condensate. It can be treated and recycled for use in water closets/urinals and irrigation systems to reduce your building’s domestic water consumption and wastewater quantity. Graywater is piped separately from the building’s main wastewater system and is routed from the designated fixtures providing graywater to a graywater treatment (if required) and storage system. The exact components of this system will depend on your manufacturer and authority having jurisdiction (AHJ) but it typically consists of a water treatment system, a storage tank, and a pump. The treated graywater will then be routed to the water closets and irrigation systems designed to be served from the graywater systems. Even though the graywater may go through a treatment system, it is important to note that this water is still not potable.

Is a Graywater System Right for Your Building?

Now that we know what a graywater system is, when is a graywater system right for your project/building? To utilize a graywater system to the fullest extent, the project should have a steady and consistent usage of the fixtures supplying the graywater system. Buildings with consistent shower and/or laundry usage provide the best supply to a graywater system. This could apply to hotels, multi-family, fitness/recreation centers, police departments, etc. Buildings without shower or laundry usage can still be a good candidate, but the graywater system may not be capable of providing the water for all the water closets or irrigation needs since the waste from lavatories will typically not equate to the water closet and irrigation usage. A review of the feasibility of a graywater system for a building can be done during the pre-design or schematic design phases with the plumbing engineer and a graywater system manufacturer to determine if it’s a good application for the project.


In conjunction with evaluating if a graywater system is suitable for your building based on building type and fixture usage, it will need to be determined that the AHJ allows graywater systems and if they have any special requirements for the system. The City of Denver, for example, allows and encourages graywater systems, but a graywater system installed in the City and County of Denver must meet the requirements of Denver’s Graywater Use Program, which can be found on the city’s website and outlines requirements for graywater systems used for irrigation and toilets/urinals. These requirements include treatment, signage, watercolor, testing, and permitting needs.


We have now determined that a graywater system is a good application for our project, and the AHJ allows graywater systems. That great! So, what is next? During the early design phase, the engineer will need to work with the architect and other consultants to ensure the proper location and space are allocated for the system. The graywater system will preferably be located in a room below the fixtures providing graywater so the waste can gravity drain into the treatment/storage system. Ideally, this would be located in a basement. The engineer will also need to determine the required system components based on the application and AHJ to ensure proper space is allocated for the equipment. The system could include treatment equipment, storage tanks, pumps, backflow preventors, valves, etc., so ensuring space is appropriately allocated for this equipment early is critical. If the proper location and space are allocated for the graywater system early, this should set up the design for the remainder of the project.

Overall, a graywater system can be a great way to conserve water usage in your building and decrease water utility costs. Prior to implementing a graywater system in a building’s design, the building’s fixture use should be evaluated for the impact of the graywater system, along with confirming the AHJ requirements for graywater systems to ensure it’s the right approach for the project.