Case Study: Whole Foods, New York

While greywater harvesting is a certainly promising tool in its own right, many successful water harvesting systems will combine solutions for both rainwater and greywater collection in order to fully meet the demands of the building. An example of this is Water Harvesting Solutions (Wahaso)‘s proposed system design for a new Whole Foods in Brooklyn, New York.

As Wahaso outlines on its projects page, the Whole Foods initially wanted to utilize recycled greywater from the facility’s lavatories for several non-potable applications – specifically, toilet flushing and irrigation. However, it soon became clear that a harvesting system that solely collected greywater wouldn’t be sufficient to meet the needs of the building. Wahaso’s solution was a “hybrid harvesting system” that would collect rainwater from the rooftop of the facility’s greenhouse as well as greywater from the building’s lavatories.

This hybrid system filters and treats both rainwater and greywater, bringing both sources up to a suitable quality for non-potable uses such as toilet flushing and irrigation. Upon completion, this hybrid harvesting system will save approximately 1.6 million gallons of water each year. Indeed, every single toilet flush at facility will use rainwater and greywater that have been collected and treated by Wahaso’s system. Furthermore, much of the building’s irrigation demands during the summer will be met by the system. In the end, it is anticipated that around 72% of the total water needs for toilet flushing and irrigation will be met by the harvesting system.

The unique project outlined here is a shining example of one way that greywater harvesting – in this case, combined with rainwater collection – can lead to substantial reductions in municipal water usage for commercial and institutional properties. Without a doubt, property owners will achieve substantial savings on their water and utilities bills after implementing a system such as the one outlined above. However, the significance of a water system such as this one goes deeper than mere monetary savings: recycling and reusing water is a way for environmentally conscious businesses and institutions to define themselves as leaders of a sustainable future.

Greywater Processing Methods

There are many ways to customize a greywater harvesting system to the unique needs of each building. The treatment process offers several options for filtering, sanitizing and storing collected greywater depending on the building specifications.

Filtration: The filtration step is a crucial step in the process, as greywater can quickly become septic if not treated right away. During this step, larger solids (usually greater that 5 microns) are removed from the water, and debris is flushed into the sewer system. Filtration options include bag filters, settling tanks or mesh screens.

Sanitation: The sanitation step ensures than water is free from algae, bacteria and viruses that could form in the tank. This can be done in one of two common methods:

  1. Chlorination can be injected into the water. This is the most common method.
  2. Ultra violet sterilizers can also be used. The light destroys the DNA in organic matter that may be present in the water.

Storage: The most commonly used storage tanks are made from fiberglass or concrete. This depends on the availability of storage space, demand and uses for the water, and turnover frequency.

Case Study: Hotel Bel Air Villas

The Hotel Bel Air Villas, located in Hollywood, California is a good example of a commercial residential building that utilizes greywater for on-site reuse.

The processing system was designed and installed by Water Harvesting Solutions to apply greywater collected from showers and sinks for application in landscape irrigation. Because of strict local water codes in the area, the water must be near-drinking quality water before it is used to ensure public safety. The captured greywater is treated with chlorine and stored in a 4,200 gallon fiberglass tank before it is pumped into the building’s irrigation lines.

The building was commissioned in January of 2012 and is projected to save 240,000 gallons of water per month, which totals 2.9 million gallons in a single year.

The Value of the NSF 350 to the Greywater Reuse Industry


As the national water crisis grows, so does interest in sustainable water practices, particularly water reuse. On-site water reuse (or harvesting) typically involves capturing and treating onsite water for reuse in applications that don’t require drinking-quality (i.e. potable) water—most often toilet flushing and irrigation.

Most people consider rainwater to be the most logical source for reuse because it’s easy to treat. But greywater offers a more predictable sources for harvesting systems, especially in areas of the country with low annual rain amounts or highly seasonal rainfall patterns. Though greywater reuse is still a new practice, there have been several advances in the greywater reuse industry that will encourage commercial building owners and contractors to consider these systems for construction.

Greywater (or “graywater”), by definition, is previously used water from showers, sinks and rinse cycles in dishwashers and washing machines. If treated properly, this can become an excellent source for toilet flushing and irrigation. But harvesting greywater also comes with a unique set of challenges, specifically with regard to the potential risk to public health with improperly treated water

By its definition, greywater contains various contaminants including soaps, chemicals and human biological waste that can pose a threat to public safety if sprayed or handled. Sophisticated greywater harvesting systems have emerged that filter and sanitize this water to bring it to an appropriate quality for reuse in toilet flushing, irrigation and other non-potable applications. But until recently, there was no widely accepted code that determined what exactly this quality should be.

In response to this need, the National Sanitation Foundation (NSF) has established the NSF/ANSI Standard 350, the first and only national certification process for both commercial and residential buildings. According to Tom Bruuersema, General Manager of NSF Sustainability, NSF-350 intends to become a national standard for greywater treatment quality that rewards quality sustainable infrastructure. “Our hope is that it gives a structure that would enable the market (industry manufacturers, regulatory code bodies and users alike) an awareness around the value of these technologies in the marketplace,” Bruuersema said.

The Standard has been accepted into local codes in the states of California, Washington and Arizona. Plumbing associations such as the IAPMO and the ICC have also given recognition to the NSF 350 as authoritative.

Greywater System Advantages

We are often asked, “Why install a greywater system?” Isn’t rainwater easier and safer for reuse? Don’t building codes restrict the use of greywater (also known as “gray water” and “graywater”). THe short answer to these questions is, “it depends”.

What are the Advantages of A Greywater System?

  • In geographies where rainwater is scarce or highly seasonal, greywater can be a dependable source of water for reuse, meeting 100% of demand for toilet flushing in a building and can meet most of the irrigation needs for a typical building.
  • Because water supply and demand are matched day by day, a greywater system needs much less storage capacity for water. A typical commercial rainwater harvesting system might need 30-40,000 gallons of storage. That is expensive (about $1.50 – $2.00 per gallon!), and it takes up a lot of space above or below ground. Conversely, a typical commercial greywater system may only need 500-1,000 gallons of storage depending on the hourly supply and demand during the day.
  • A greywater system helps reduce the load on a municipal water treatment system since the water is used twice. Greywater used for toilet flushing reduces the demand on the municipal sewer system by 50%. And if that harvested greywater is used to irrigate landscaping, it can reduce all that water that would need energy used for pumping and treatment.

What are the Disadvantages of a Greywater System?

  • Greywater is inherently more troublesome than rainwater to properly treat for safe reuse. Do you ever pee in your shower? Wash really dirty hands in the sink? Then there are the soaps and cleaners we use in sinks and showers. The net is that (while heavily diluted) greywater can have a lot of contaminants and pathogens that must be removed or stabilized to make the water acceptable for reuse. That requires a system that is properly designed and maintained.
  • Greywater systems can be more expensive to maintain. Additional chemicals and filtration are needed that require maintenance and consumable supplies – and those cost more than what is typically needed to process rainwater and other cleaner on-site sources.
  • Because greywater needs special treatment or can quickly turn to blackwater, many local codes severely limit or prohibit its use. That doesn’t mean that a properly designed system cannot seek a code exception at the local level – just that the approval process can be longer or more costly.

At the end of the day, a greywater harvesting system may or may not be right for your project or property. If you have an interest in a greywater system, you should speak with an industry expert like Water Harvesting Solutions. They can evaluate supplies and demands and recommend a system that is best for your situation.

What is Greywater?

The term greywater most often refers to the gently used water from a building’s showers and sinks, but it can also include water from the rinse cycle of washing machines and dishwashers.

Greywater can be treated and used for applications that don’t require drinking quality (aka “potable”) water, like toilet flushing and lawn irrigation. While rainwater is generally the most common water source for reuse, greywater harvesting is especially practical in dry areas with low rainfall that don’t produce enough rainwater for reuse. Greywater harvesting differs in that it requires much less storage, but it also means that it must be treated and sanitized to a greater degree to rid it of soap and other contaminants commonly found in greywater. Systems have emerged that treat collected greywater so it’s an appropriate quality for reuse. Greywater harvesting is an excellent option for water savings in large residential buildings like dormitories or hotels, which are large producers of greywater.

It should be noted that greywater significantly differs from blackwater, which contains human biological waste. Blackwater cannot be used for harvesting.


Rainwater Harvesting System | Commercial Rainwater Harvesting | Greywater System