How can gray water be recycled?

gray water treatment

It is a widely recognized fact that the world's population is increasing and, unfortunately, our current way of life does not promote responsible water consumption. On the contrary, it aggravates the situation. If the population continues to grow at the current rate, reaching 7.400 billion today, it is projected to reach 9.200 billion by 2050. This will result in unprecedented demand for drinking water that will be incredibly high and unsustainable. In fact, according to the most recent United Nations report, a staggering 7 billion people will experience water scarcity by 2050. Thus, the question arises. how gray water can be recycled to optimize water use.

Therefore, in this article we are going to tell you how gray water can be recycled and what to do with it.

Gray water recycling: a sustainable alternative

gray water recycling

Greywater, as commonly understood, refers to the sewage water domestic waste produced in a home, covering activities such as washing dishes, washing clothes and using the bathroom, excluding toilet water. It is important to note that gray water contains a lower amount of contaminants compared to normal wastewater, making your treatment process easier.

The reuse of gray water for purposes such as garden irrigation or filling toilet cisterns has significant value in terms of environmental preservation and resource conservation. Greywater purification not only offers important environmental benefits but also leads to a reduction in consumption, which makes it a very advantageous practice.

However, let's look at it in a more simplified way. In a household made up of 4 people, approximately 600 liters of water are generated per day. By using gray water, we can recycle enough water for an entire year for sanitary use (38.000 liters) and daily garden irrigation (through 100 drip points). Besides, We contribute approximately 140.000 liters of high quality water to the environment.

Benefits of gray water recycling

How can gray water be recycled?

Resource Conservation

Greywater, after undergoing adequate treatment, offers a viable and efficient alternative for various daily uses that do not require the use of potable water. These include, but are not limited to, toilet flushing, irrigation and cleaning. Implementing appropriate technologies it is possible to reduce drinking water consumption in our buildings by up to 40%, as stated in the Spanish Technical Guide of Recommendations for Gray Water Recycling in Buildings. The versatility of treated gray water extends to a wide range of environments, including single and multi-family homes, hotels, sports centers, industrial buildings and expansive areas.

pollution reduction

Regarding treatment systems for gray water reuse, there are several options available, including physical, physical-chemical and biological methods. Furthermore, there is even the possibility of direct reuse without prior treatment, using basic devices to collect and distribute gray water to the intended points of use with minimal or no storage.

Economic savings

Implementing this habit in our homes does not require a significant financial investment and the benefits are numerous and immediate. Similarly, the utilization of greywater can lead to substantial reductions in water consumption within the industrial sector, which is highly dependent on this resource. In many cases, It is enough to use treated and recycled water for common processes such as cleaning.

Gray water recycling process

water filtration


Greywater collection is typically carried out in the home, at points where wastewater not contaminated by fecal matter is generated, such as sinks, showers, and washing machines. These waters are directed to a collection system separate from black water (contaminated by fecal matter), often through additional pipes or diversion devices. It is important to ensure that these waters do not mix with sewage to maintain their quality and facilitate subsequent treatment.


Once collected, gray water is subjected to a treatment process to eliminate impurities and contaminants that may affect its quality and safety for reuse. The treatment consists of several stages, which include filtration to removing solid particles, disinfection to eliminate pathogenic microorganisms, and removal of chemical compounds through advanced oxidation or adsorption processes. Depending on the quality standards required and the intended use of the recycled water, different technologies and treatment systems can be used.

Storage and distribution

Once treated, gray water is temporarily stored in tanks or cisterns specifically designed for this purpose. These storage systems include water quality control devices to monitor and maintain water integrity. The recycled water is then distributed for a variety of non-potable uses, such as garden watering, toilet flushing, vehicle washing, among others. It is essential to ensure that the distribution system is properly designed and maintained to avoid cross-contamination with drinking water or black water, as well as to ensure the safety and effectiveness of the use of recycled water.

Practical applications of recycled gray water

Garden irrigation and landscaping

Irrigation of gardens and green areas is one of the most effective applications of recycled gray water. This type of water, properly treated to eliminate impurities and pathogens, It can be used to water plants, grass and other plant elements in residential gardens, public parks and recreational areas. The use of gray water in irrigation reduces the demand for potable water for non-potable purposes, helping to conserve water resources and maintain vegetation in optimal conditions without compromising the quality of the landscape.

toilet flush

Recycled gray water can also be used in toilet flushing systems, helping to reduce drinking water consumption in the home and other commercial or institutional settings. By installing dual plumbing systems or specific treatment equipment, treated gray water can be used to fill toilet tanks, partially or totally replacing the drinking water that would normally be used for this purpose.


Vehicle washing is another practical application of recycled gray water, which can be implemented in homes, service stations, car wash companies, and commercial vehicle fleets. Treated gray water can be used in high-pressure washing systems or manual systems, providing a sustainable alternative to the use of drinking water to keep vehicles clean and in good aesthetic condition.

I hope that with this information you can learn more about how gray water can be recycled.

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