When it comes to saving water, specifically in areas affected by droughts, reclaiming water from showers and sinks can positively benefit your facility. However, wanting to save water is not the only factor to consider when deciding if a greywater reclamation system is right for your facility.

Prior to designing the greywater system, the first step is to understand if reclaiming greywater will contribute to reducing your building’s water usage. This process is known as a “water balance calculation” or an evaluation of the return on investment.

Most would say greywater systems are only used to minimize the water consumption of a building throughout the building’s life span. There are some projects whose objective of greywater reclamation is to satisfy partial water demand of the building, such as flushing toilets and urinals. However, it is important to know and estimate the amount of greywater to be treated based on the purpose and demand of the recycled water.  It is vital to not treat more than the needed demand, because every gallon of water treated has cost associated with it.

Likewise, it is important to know the building occupancy and fixture flow rates to estimate the amount of water being used in the building. In order to do so, the gallons of greywater to be collected daily from the building’s sinks, lavatories, and showers need to be estimated. In addition, the average daily demand of the reclaimed water to be used in the building should be estimated.

The water treatment system is sized based on the daily average usage. For instance, 5,000-gallons of greywater can be collected daily; however, the demand of reclaimed water in the building is, on average, 2,000-gallons each day. Therefore, if a water treatment system is to be installed in the building, it should be designed based only on the 2,000-gallon capacity. This estimation is based on the average daily demand, and is not derived using a calculation based on fixture units — a fixture unit calculation is typically used for pipe sizing only and addresses the peak demand, which will exceed the actual average daily usage.

Ultimately, the minimum requirement for an on-site water treatment system is recommended to meet or test to the National Sanitation Foundation 350 standard under the Uniform Plumbing Code jurisdiction. However, local water agencies often have additional rules and regulations regarding greywater treatment systems. It is essential to research and understand the limitations and requirements prior to incorporating a greywater system into the building.

In addition to the average amount of water reclaimed and local plumbing codes, how the water will be treated is an additional factor to consider.  The main considerations in treatment of greywater are pathogens (especially viruses and protozoa), nutrients, salts, plumbing.

There are multiple engineered treatment systems available on the market, however different treatment methods require different components and treat water to different levels of purity. Interviewing various manufacturers to better understand their preferred treatment method and how it will work with your facility’s design and local jurisdiction standards can aid in ensuring the water quality requirements and demands are met. Typical components involved with water treatment systems, include: collection and storage tanks (treated or untreated), treatment plants, overflow drain, by-pass water makeup, pumps, dual plumbing systems (for both greywater collection and distribution), and the footprint of the system.

These are only a few factors to consider when deciding on your plumbing system. It is also important to consider the average amount of water reclaimed and local plumbing codes, as well as how the water will be treated.



  • Zay Soe

    Senior Design Engineer

    As a Senior Design Engineer, Zay Soe is responsible for the planning and designing of plumbing systems for administrative offices, healthcare, and government facilities. With over seven years of experience, he has designed multiple plumbing and medical gas systems and has earned responsibility for building plumbing load analyses, equipment selection, and preparing completed construction documents for all plumbing work.

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