Graywater recycling

This technology enables efficient management of wastewater from everyday building operations by capturing greywater, treating it and then reusing it as non-potable (service) water.

Greywater comes mainly from everyday use such as showering, handwashing and laundry, and it represents a significant volume of water that can be reused after treatment. Unlike sewage (blackwater), it does not include toilet waste or kitchen waste, which makes it easier to treat and reuse within the building.

In the Czech Republic, greywater recycling is well suited to public-sector buildings, especially regional authority buildings and publicly funded organisations such as schools, healthcare facilities, social services and administrative buildings. These buildings produce a steady and sufficient amount of greywater, which allows the system to run efficiently.

The solution responds to the need to reduce drinking water consumption, adapt to climate change and make public buildings more sustainable to run. It also fits with ESG trends and circular resource management in public infrastructure.

Using greywater depends on keeping the drinking water and non-potable water pipework separate, which must be planned during the design or renovation stage of the building.

The solution is based on a system that collects, stores, treats and distributes greywater within the building. Its core is a separate drainage system that captures greywater from sources such as showers, bathtubs, washbasins and washing machines and carries it to a storage tank. Storage must be designed so that water is held for no longer than 24 hours, which limits any decline in its quality.

The water is then treated to remove pathogenic microorganisms and organic matter that could pose hygiene risks or cause biofilm to grow in the pipework. The system always includes disinfection of the treated water and quality monitoring. The treated water is then used as non-potable water, typically for flushing toilets or other operational purposes inside the building. The drinking water and non-potable water pipework must be kept strictly separate.

Typical technical features of this solution include separate pipe systems for greywater and drinking water, storage tanks sized to match how much water is produced and needed, treatment technology, and a water quality monitoring system that meets the requirements of the regional public health authority. The solution can also be combined with rainwater harvesting and use, which further improves the building’s overall water efficiency.

For the building’s owner or manager, it is essential to consider greywater recycling during the design or renovation stage. Key factors include the layout of the pipework, the sizing of the technology and making sure the system can be run over the long term. The project must also be reviewed by an authorised professional and include a risk analysis and an operation and maintenance plan, with regular water quality monitoring.

Limitations of the Innovation

The main limitations and barriers include greater demands on design and coordination of technologies than with standard systems. Installation requires separate pipework, space for the equipment and strict compliance with hygiene and technical standards.

A significant constraint is the legal framework, which currently allows treated greywater to be used mainly inside buildings. Another factor is operating demands: the system needs regular maintenance, quality monitoring and professional management, which can be challenging especially for smaller organisations without technical staff.

The economic barrier is the higher upfront cost of installing the technology and making construction changes. Over the long term, however, these costs are offset by water savings and reduced strain on the sewer infrastructure. For successful implementation in regional authority buildings and publicly funded organisations, it is therefore essential to prepare the project well, size the system appropriately and set up a stable operating model.

 

Prepared by ICOK, 2026

Source: Bartáček, J.; Stránský, D. (2025): Metodický postup problematiky recyklace šedých vod v sídlech ČR [Methodological Guidance on Greywater Recycling in Czech Municipalities]. State Environmental Fund of the Czech Republic.