Greywater: A promising method for fostering water conservation in green buildings

Rand Water is dedicated to supporting both industries and communities in becoming conscientious water consumers. This commitment is exemplified, in part, by its Water Wise brand. Beyond educating on various facets of water conservation, the brand delves into pioneering methods and techniques for promoting responsible water usage.

Water scarcity is becoming a worldwide issue rather than a remote worry. This precious resource continuously experiences huge pressure because of aspects such as population growth, urbanisation and increased climate change effect. According to the International Water Management Institution, the urban water demand is forecasted to increase from 1995 to 2025 by 62%. With these pressures, water shortage is likely to manifest in 2050. For these reasons, it has become imperative that we find adaptable solutions in which we can maintain the existing water resources, while seeking methods in which we can reduce the demand of potable water.

Greywater reuse is receiving more traction as a solution to urban water management as it offers a straightforward, but effective, option to shift our water-use patterns. Greywater reuse is significant because it simultaneously addresses two urgent issues: environmental sustainability and water scarcity. Adopting greywater methods is a critical step towards a future where we are more water-conscious and resilient. In the face of an unpredictable climate context, water reuse is a commitment to protecting our most valuable resource, whilst supporting business and community sustainability.

What is Greywater?

Greywater is wastewater that can be reused for other purposes. Greywater makes for as much as 70% of all residential building’s water use. Although greywater and blackwater are typically combined, by separating the two, greywater on its own provides several reuse opportunities such as toilet flushing and garden irrigation. This can assist in lowering potable water use in wet-stressed areas by up to 30% for households and up to 60% for corporate buildings. Furthermore, saving money on garden irrigation through reuse can boost household savings by 40%. Blackwater, on the other hand, is toilet water that contains faecal matter and urine. Faecal matter is a breeding ground for harmful bacteria and pathogens that can cause diseases. As a result, this requires a specialised treatment process for onsite use. Greywater can be collected from the source by installing a plumbing system from an outlet of bathrooms/kitchens to a garden or for toilet flushing. To this end, a greywater treatment system such as constructed wetlands and green walls can be installed to help filter large particles, nutrients and pump-treated water through irrigation pipes.

Benefits of Greywater in Green Buildings

Water conservation: The use of greywater provides us with an opportunity to use an average of approximately 35 – 234 litres (per person per day) of greywater, which can be repurposed for garden irrigation or toilet flushing where little human contact is achieved.

Enhancing the EDGE (Excellence in Design for Greater Efficiencies) standard: The incorporation of a greywater reuse system can play a pivotal role in diminishing the reliance on potable water, consequently elevating the overall EDGE score of the building.

Cost-effectiveness: The use of greywater is inexpensive, and for this reason, water bills can be drastically reduced while investing in a greener future.

Lush landscapes: Watch your garden flourish! Greywater provides essential nutrients such as total nitrogen (2.75 to 21.00mg/L) and total phosphorus (0.062 to 57.00mg/L) that mainly originate from the kitchen (kitchen residues/waste) and hand basins (soap), respectively. These nutrients nourish our soil and plants, promoting healthier growth and vibrant blooms.

Resilience to drought: Water-efficient measures (greywater reuse) make green buildings more resilient to water scarcity and drought conditions, ensuring continued operations during challenging times.

Safe and Sustainable use of Greywater

• Greywater has been shown to be a potential hazard to human health. Its handling must be done with care to reduce the risk of infection. Use gloves when handling greywater.
• Greywater that contains potentially infectious pathogens should not be used for irrigation. This includes water used to wash nappies or soiled sheets.
• To reduce odour and bacteria, greywater should be used within 24 hours of collection.
• Subsurface irrigation is the best way of watering as it protects against possible microbiological health hazards.
• To avoid waterlogging and prevent possible root damage, it is critical to disperse greywater uniformly in your landscape.
• When irrigating with untreated greywater, it is not advisable to use spray irrigation. This is primarily due to the increased risk of exposing people to greywater.
• Where possible, greywater should not be used for an extended period in the same area. This may in some instances result in the accumulation of different components found in greywater that may negatively impact the health of plants.