Water is used throughout our homes and buildings every day. We shower, wash our hands, do laundry and flush toilets, often using high-quality drinking water for all of it.
But not every use requires drinking-quality water.
Greywater recycling is the process of collecting, treating and reusing lightly contaminated water from sources such as showers and baths. Instead of sending this water directly to the sewer, a greywater recycling system treats it so it can be safely reused for non-drinking purposes, such as flushing toilets, doing laundry or irrigating a garden, depending on the system and local regulations.
By using the same water more than once, homes and buildings can reduce their demand for drinking water without requiring people to change their daily routines.
What is greywater?
Greywater, also written as graywater, is wastewater that has been used but does not contain toilet waste.
Common sources of greywater include:
- showers
- baths
- bathroom washbasins
- washing machines, depending on the recycling system
Water from toilets is known as blackwater and requires a different type of treatment.
Kitchen wastewater is also often treated separately because it can contain higher levels of fats, food particles and other contaminants.
Greywater sits somewhere between fresh drinking water and heavily contaminated wastewater. That makes it particularly interesting for local water recycling.
What is greywater recycling?
Greywater recycling means treating greywater so that it can be used for a second purpose within a home or building.
For example, water used for a morning shower would normally disappear down the drain and enter the sewer system. With a greywater recycling system, that water can instead be collected and treated before being made available for another suitable use.
This creates a local water cycle inside the building:
Use water → collect greywater → treat it → store it → reuse it
Rather than using drinking water once, a building can make better use of the water already available.
How does a greywater recycling system work?
The exact treatment process depends on the technology being used, but a greywater recycling system generally follows several steps.
1. Greywater is collected
Water from selected sources, such as showers and baths, is directed towards the greywater recycling system instead of immediately entering the sewer.
2. The water is treated
The system removes contaminants and treats the collected water so it is suitable for its intended non-potable uses.
Different greywater systems use different treatment technologies and levels of automation.
3. Treated water is stored
Once treated, the recycled water can be kept available until it is needed elsewhere in the building.
4. The water is reused
The treated greywater can then replace drinking water for applications that do not require potable water.
A well-designed system manages this process automatically, making water reuse part of the building's infrastructure rather than something occupants need to think about every day.
What can recycled greywater be used for?
Treated greywater is not intended for drinking, cooking or other applications that require potable water.
Instead, depending on the system design and local requirements, recycled greywater can be used for applications such as:
- toilet flushing
- washing machines
- garden irrigation
- other suitable non-potable applications
This is important because a considerable part of the water used in a building does not necessarily need to be drinking quality.
Greywater recycling allows potable water to be reserved for the applications where it is actually needed.
What are the benefits of greywater recycling?
Lower drinking water consumption
One of the main advantages of greywater recycling is a reduction in potable water demand.
Instead of continuously supplying new drinking water for toilets, laundry and other non-potable applications, some of these needs can be met with water that has already been used elsewhere in the building.
More efficient use of available water
Greywater recycling changes the traditional linear approach to water.
Instead of:
supply → use → drain
water can become:
supply → use → treat → reuse
It is a more circular approach to one of our most important resources.
Less wastewater
Reusing water locally also means that less water is immediately discharged from the building as wastewater.
This can reduce the amount of water entering wastewater infrastructure and helps buildings manage water more intelligently at the point where it is used.
Greater water resilience
Water availability is becoming an increasingly important consideration for homes, cities and businesses.
Recycling water locally can reduce dependence on a continuous supply of potable water for applications where drinking-quality water is unnecessary.
For larger developments, hotels and other buildings with significant water demand, this can form part of a broader water resilience strategy.
Better building performance
Buildings are becoming smarter in how they manage energy, heating, ventilation and other resources. Water can be managed intelligently too.
Integrating greywater recycling into a building can support sustainability objectives and help designers, architects and developers create more resource-efficient, future-ready buildings.
Water savings without changing everyday habits
One of the most practical benefits of automated greywater recycling is that it can operate in the background.
People can continue to shower, use the toilet and do their laundry as usual. The difference is in what happens to the water behind the scenes.
Effective water conservation does not always have to mean using less. It can also mean using what we have more intelligently.
Greywater recycling vs rainwater harvesting
Greywater recycling and rainwater harvesting are both ways to reduce potable water consumption, but they use different water sources.
Rainwater harvesting collects rainfall, usually from roofs, and stores it for later use.
Greywater recycling reuses water that has already been used inside the building, such as shower or bath water.
The two systems can complement each other.
Rainwater availability depends on weather, storage capacity and the size of the collection area. Greywater production is linked more directly to how occupants use water within the building.
For some projects, combining multiple water sources can help create a more resilient water strategy.
Is greywater recycling safe?
Greywater should not simply be collected and reused without appropriate treatment.
A purpose-built greywater recycling system is designed to treat and manage the water before it is reused. System design, installation, maintenance and the intended application all play an important role.
Requirements for greywater reuse can also differ between countries and regions, so systems should be designed and installed according to applicable local standards and regulations.
Can greywater recycling be used in homes?
Yes. Greywater recycling can be integrated into individual homes as well as larger buildings.
The possibilities depend on factors such as the plumbing configuration, available space, water consumption and intended reuse applications.
Integrating water recycling during the design or construction of a building can make implementation particularly straightforward because the necessary pipework can be planned from the beginning.
Greywater systems can also be considered for renovation and retrofit projects, although the feasibility will depend on the existing building.
Greywater recycling in larger buildings
Greywater recycling becomes especially interesting in buildings where water use is predictable and repeated every day.
Examples include:
- apartment buildings
- hotels
- student accommodation
- gyms and sports facilities
- commercial buildings
- residential developments
A hotel, for example, can generate significant amounts of shower water while simultaneously requiring water for toilets, laundry and other non-potable purposes.
Instead of treating these as two completely separate demands, water recycling allows part of one to supply the other.
How Hydraloop approaches greywater recycling
Hydraloop develops intelligent water recycling systems for homes and buildings.
Hydraloop systems collect and treat water from sources such as showers and baths and make the recycled water available for suitable non-potable applications.
The process is designed to work automatically in the background, making water reuse part of the building infrastructure while allowing occupants to continue their normal routines.
Rather than viewing water recycling as an additional sustainability feature, Hydraloop sees it as part of the next generation of intelligent building infrastructure: technology that helps buildings manage water locally, efficiently and automatically.
Is greywater recycling worth it?
Whether a greywater recycling system is suitable for a project depends on factors including water consumption, building type, local water conditions, regulations and the intended applications for recycled water.
However, the basic principle is simple.
We currently use high-quality drinking water for many applications that do not require it, while water that could potentially be reused is discharged after a single use.
Greywater recycling provides an alternative.
By treating and reusing water locally, homes and buildings can reduce potable water demand, use available resources more efficiently and become better prepared for a future in which intelligent water management plays an increasingly important role.
Frequently asked questions about greywater recycling
What does greywater mean?
Greywater is wastewater from sources such as showers, baths and washbasins that does not contain toilet waste. Depending on the system, water from washing machines may also be included.
What is a greywater recycling system?
A greywater recycling system collects, treats and reuses greywater within a home or building. The recycled water can then replace potable water for suitable non-drinking applications.
Can you reuse shower water?
Yes. With an appropriate greywater treatment system, shower water can be collected, treated and reused for suitable non-potable applications such as toilet flushing.
Can greywater be used for toilet flushing?
Treated greywater can be used for toilet flushing in appropriately designed systems, subject to applicable local requirements.
Can you drink recycled greywater?
No. Greywater recycling systems for buildings typically produce water intended for non-potable applications, not drinking or cooking.
What is the difference between greywater and blackwater?
Greywater comes from sources such as showers and baths. Blackwater contains toilet waste and requires a different level and type of wastewater treatment.
What is the difference between greywater recycling and rainwater harvesting?
Rainwater harvesting collects precipitation, generally from a roof. Greywater recycling treats water that has already been used inside a building. Both can help reduce demand for potable water.
Does greywater recycling require people to use less water?
Not necessarily. Automated greywater recycling focuses on using water more efficiently by using some of it more than once. It can therefore reduce potable water demand without requiring major changes to everyday routines.