Grey Water Harvesting Systems

Wahaso Grey Water Harvesting Systems

Greywater (also referred to as graywater, grey water, and gray water) is “gently used” water captured from showers, lavatory sinks, laundry, and light commercial processes. It can often be an excellent source of water, saving thousands or even millions of gallons of water per year.

Greywater Harvesting

Given the contaminants inherent in greywater, it is important that any grey water systems are designed properly. Wahaso’s grey water recycling systems for commercial properties has been certified to meet both IAPMO 324 and NSF/ANSI 350 standards.

The Wahaso greywater harvesting system has been tested and proven to provide a safe, treated supply of water that can be used for a variety of non-potable applications.

Greywater is gently used water from sinks and showers. It may also include washing machine water. Greywater contains fewer contaminants than domestic wastewater, making it safer to handle and easier to treat and use in irrigation, toilet flushing, cooling tower make-up and other non-potable applications. Once greywater is properly treated and processed with a greywater harvesting system it is called on-site treated non-potable water.

Grey Water Recycling Systems Design

The proprietary treatment train of Wahaso’s greywater system provides an astonishing level of treatment. Raw greywater is pre-filtered before being sent to a collection tank or sump. Wahaso’s grey water systems for commercial buildings pre-filtration helps to keep the collection tank/sump clean, and additionally, Cupridyne® is added to the tank/sump to reduce odor. The certified treatment grey water filtration system includes filtration down to 0.02 microns, which removes suspended solids as well as bacteria and viruses. Filtered water is sanitized using Ultraviolet (UV) and, if required, chlorine and is then sent to the end use or stored in a processed water holding tank to await re-pressurization. The Wahaso UF system Treated Greywater is safe and suitable for non-potable applications such as toilet flushing, irrigation and cooling tower make-up.

IAPMO 324 and NSF/ANSI 350 Certified

A system with third-party certification can provide peace of mind that a system is reliable and safe. The Wahaso greywater system is certified for both IAPMO 324 and NSF/ANSI 350, meeting or exceeding all the requirements for each standard.

GW-UF35-50, GW-UF70-100, GW-UF140-150 and GW-UF210-210 are certified by IAPMO R&T against NSF/ANSI 350 and IAPMO IGC 324.

Water Harvesting Solutions utilizes a number of leading-edge filtration, sanitation and monitoring steps to bring the water to near-potable quality, eliminating health and aesthetic concerns while meeting the regulatory requirements of most communities. Our GW-Series of processing systems and filtration skids have been field tested and are compliant with the National Sanitation Foundation NSF/ANSI-350 Standard for commercial graywater processing systems.
It is important to note that the term “greywater” refers to untreated water from showers and sinks. Once the greywater has been filtered and sanitized – its classification changes from “greywater” to “on site treated non-potable water” and it is then safe to store and utilize for many purposes.

System Benefits

  • Fully Automatic Processing. Raw grey water is treated as it is generated to minimize the growth of harmful pathogens.
  • Low Maintenance. The system has been designed to run reliably for long intervals, with minimal maintenance required.
  • Scalable. The Wahaso greywater system can be scaled to treat from 2,000 to 200,000 gallons per day or more.
  • Robust Controls. Wahaso’s proprietary control system is custom programmed to monitor and track all system activity.
  • Integrated System Design. Wahaso’s greywater processing skids are pre-assembled and integrated into comprehensive system designs that include all pumps, storage, filtration, sanitation, and controls.

Standard Systems

Wahaso’s greywater system is fully scalable and able to process 2,000 – 200,000 gallons per day. Each standardized system includes filtration and sanitation equipment. The customizable equipment includes tanks, pressurization, and controls.

For more information on our greywater harvesting systems, download the information sheets.


Greywater is collected from showers, baths and sinks through a plumbing system that is separate from toilets and urinals – which produce “black water”. Greywater should be treated almost immediately to stabilize it and prevent it from going septic. Untreated greywater should never be stored more than a few hours.
1 Filtration Stage
The first filtration step is designed to quickly stop biological activity and remove the larger particulates inherent in shower and sink discharges. This is accomplished in a settling tank stage, where chlorine or another oxidizing agent is added to immediately begin reducing bacteria in the greywater. After a set contact and settling time, the treated greywater is pumped through the GW-Series filtration skid.
2 Filtration Stage
For commercial systems, the next filtration stage uses a self-cleaning disk filter that can effectively handle hair and other greywater solids. Particulates greater than 80 microns in size are removed and sent to the sewer system. The next stage uses a multi-media filter that removes all particulates greater than 5 microns in size. The filter minimizes maintenance by automatically going through a backwash step that flushes debris to the sewer system and the resets the multiple levels of filtration media. Activated charcoal is the final filtration step, “polishing” the water to make it crystal clear and free of any odors. Treated water is then ready for reuse and stored in the Processed Water Holding Tank (PWHT) awaiting pressurization to flush toilets, irrigate landscaping or support evaporative cooling systems.
3 Filtration Stage
Water quality in the PWHT is usually maintained by adding a small amount of chlorine so that a residual will protect the water in the tank and downstream to fixtures.


It is necessary to sterilize the water to keep algae, viruses, bacteria and other organic contaminants from forming in the storage tanks. There are several technologies available for this purpose.
Because of the higher contaminants inherent in greywater, residual sterilization capacity is valuable in keeping the entire system clean. Chlorine sanitation is the most common method to achieve this. Depending on the type of system, we will recommend chlorination delivered to the system in 50-gallon drums by a local chemical supplier. The chemical is similar to that used in a municipal water treatment systems.
Ultra Violet Sanitation
Some greywater systems use ultraviolet sterilizers that expose the water to a specific wavelength of UV light that destroys the DNA of organisms present and keeps the water sterile. Sizing of the UV system is critical to maintain sufficient exposure rates to keep the water sterile. The advantages of UV sterilization are that it uses no chemicals to kill pathogens, requires minimal maintenance and is significantly less expensive than chlorination systems. It’s biggest disadvantage is that the UV light can only kill pathogens that are directly exposed to the tubes – and there is no residual killing capability like chlorine. If the water is cloudy, as is common in untreated greywater, U.V. is ineffective as a sanitizer.


Storage of the treated greywater is determined by the demand and uses for the water, available greywater volume and turnover frequency, and space to locate the tanks. For more information on the options for storing rainwater and greywater, see our Water Storage page.

All storage systems have a connection to a municipal source so that toilet flushing and other uses can occur even if there is not an adequate supply source of greywater. An air gap inlet can automatically be turned on to make-up water in the treated tank should a supply problem develop in the greywater harvesting system. In typical applications of a greywater system for toilet flushing, there is more than enough supply of greywater from showers and baths to meet flushing requirements.

Wahaso tank systems can be pre-mounted on skids for ease of installation with all internal piping manifolds and sensors mounted and pre-tested at our fabrication center. All of our polyethylene tanks are rated for potable water even though we are not using this water for drinking purposes.

Application of Greywater

A repressurization system is required to move the greywater to toilets or other applications throughout the building. In commercial systems, pump skids are duplex, with two identical commercial grade pumps in tandem with each rated at 70% of peak demand. The operating system alternates demand between the two pumps; if a high demand situation occurs, both pumps can be made available. And if one pump should fail, the system will continue to provide harvested water.

We work closely with building engineers to properly size the pumps so that adequate pressure (PSI) and volume (GPM) is available at the farthest – and highest altitude – end point in the system.

Greywater System Monitoring And Control

Water Harvesting Solutions employs programmable logic controllers (Allen-Bradley as standard) that fully automate and control the entire process for greywater harvesting. Our proprietary software is customized for each application and provides the capability of interfacing with most building automatic systems and other alarm and condition monitoring including Modbus™ or BACNET™.

In addition to monitoring the system mechanicals, the control system can track the amount of water in each tank and track and display the monthly amount of water harvested. An interface allows remote monitoring via a web page for maintenance or educational purposes. Wahaso can use the remote access to help a building maintenance staff diagnose potential system problems.

Ongoing Maintenance

Wahaso’s greywater harvesting systems are engineered to meet the rigors of commercial and institutional use. Fully automated, Wahaso’s greywater harvesting systems are designed to operate independently and efficiently. Equipment skids are built using industrial-grade UL listed approved components. We warrant the entire system for one year; should a component need replacement beyond that period, it can usually be replaced with a readily available part by any qualified plumber or maintenance staff.

Wahaso Grey Water Systems FAQ’s

To learn how greywater harvesting might be used in your building project, please contact us.

1. What type of water is considered greywater?
Greywater is gently used water from sinks and showers. It may also include washing machine water. Greywater contains fewer contaminants than domestic wastewater, making it safer to handle and easier to treat and use in irrigation, toilet flushing, cooling tower make-up and other non-potable applications. Once greywater is properly treated and processed with a greywater harvesting system it is called on-site treated non-potable water.
2. What is the difference between rainwater harvesting and greywater harvesting?
Rainwater comes from roof surfaces —it is filtered and stored in a cistern for later use. Rainwater harvesting involves a system comprising spouts, cisterns, and pumps. On the other hand, greywater has already been used in a building and normally goes down the sewer line. Its harvesting system includes a series of filters, pumps, timers, sensors, and valves integrated into the existing plumbing system.
3. How do you harvest greywater?
Harvesting greywater starts with collecting it from sinks, baths, and other sources. You then feed the greywater into the greywater harvesting system for filtration and pumping into storage tanks. The filtered water stays in the tank until there is a demand.
4. Is greywater good for the environment?
Greywater may look dirty, but it is good for the environment. It is a safe and cost-effective source of irrigation water as it is rich in nutrients that promote plant growth.
5. Are greywater systems worth it?
Greywater water systems are generally a worthy investment. Grey Water Recycling Systems can reduce water usage by as much as 50%, and a system can pay for itself in three to five years. Typical greywater projects that collect sink and shower water can typically offset 125% of their toilet flushing demand. Many businesses use greywater harvesting systems for their quick return on investment. These systems also require relatively low maintenance.
6. Can you filter greywater for drinking?
While filtered greywater looks clear, it is generally unsafe for human and animal consumption. We believe that wastewater treatment plants do a good job of making drinking water. A lot of water in a building does not need to be potable and the cost to generate non-potable water is much less. Additionally, if a system designed for generating potable water is not properly maintained there can be a risk of accidental ingestion of unsafe water.
7. Can you store greywater?
The longer you store greywater the more the bacteria and other contaminants grow inside it and make it harder to treat. In a proper greywater system the greywater is filtered, sanitized and then stored for reuse. If it sits in a holding tank after processing it must then be cycled through past a UV or dosed with chlorine to keep it safe and clean.
8. Which plants can I water with greywater?
We don’t recommend watering any plants with greywater as, by definition, greywater is untreated water from sinks and showers. Once that water has been processed and properly treated it is called on-site treated non-potable water. This water source can be used for any type of vegetable, flower, grass, tree or shrub. It is even used for swimming pool make-up water.
9. Can I use greywater if I have a water softener?
Water softeners usually contain salts to bind with the metals in the water, softening the water. Such greywater is high in salts that can harm soil and plants, making it unsuitable for reuse in the environment. Depending on your system’s setup, you can bypass some appliances from the softener and reuse that portion of your greywater.
10. What is the difference between stormwater harvesting and greywater harvesting?
Stormwater harvesting uses water that is collected at grade such as from rain falling on walkways and parking lots. It has contaminants such as oil, dirt and leaves that must be removed for proper reuse. Greywater is gently used water from sinks and showers that is processed and reused.
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Since 2004

Wahaso Mission

Our mission at Wahaso is to help municipalities and commercial property owners reduce the impact of their buildings on the environment through innovative and sustainable water practices.