What is a Grey Water System?

by Team Tradify, February 8, 2024

Grey water recycling is a sustainable plumbing practice that’s growing in popularity among both private homes and large-scale commercial buildings. Grey water refers to water supplied from sources such as showers, sinks, and washing machines, which hasn't had contact with major contaminants. By implementing grey water recycling systems, this water can be treated and reused for other purposes, such as landscape irrigation or to flush toilets. Learning how to install grey water systems allows plumbing businesses to offer an environmentally conscious plumbing option within their services.

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Benefits of a grey water system
Limits to using grey water
Things to check before installing a grey water system
Types of grey water systems
Looking to the future

1. Benefits of a grey water system

Grey water recycling reduces the demand for freshwater supplies and minimises the environmental impact of wastewater disposal. Globally, wastewater management makes up over half of a typical household water bill, with 60% of a typical American household's water bill based on the management of wastewater. Combined with growing concerns of a global water shortage, there are significant financial and environmental benefits to recycling water.

Grey water recycling systems can save a household up to 40,000 gallons a year.
According to the Environmental Protection Agency (EPA), grey water recycling reduces the use of freshwater for irrigation by up to 50%.
Recycling grey water reduces the chemicals needed for wastewater treatment.

2. Limits to using grey water

Grey water offers a great opportunity to minimise waste by reusing water for tasks that don't require potable water. However, installing a grey water system requires an understanding of local laws and the requirements of individual residences.

Grey water refers to water that is ‘gently’ used. In practical terms, this refers to water that has no contact with human or animal waste, grease, oil, food or other significant contaminators. Any water source included in a grey water system must be monitored to avoid contact with contaminants.
Grey water systems require any users who come into contact with the water to abstain from using unsuitable chemicals or detergents with high sodium levels, particularly if the water is to be used in irrigation.

As a rule, grey water cannot be stored for more than 24 hours. After 24 hours, stored untreated grey water stored may:
- Turn septic
- Start to smell
- Grow microorganisms
- Breed mosquitoes.

It is usually a legal requirement to have the option to divert grey water to the sewerage system, in case it's not practical to use it within 24 hours or when it comes in contact with waste or chemicals.
Grey water must not cause any danger, or be a health hazard or nuisance to the occupants or the public. This means any irrigation systems must be contained to the residence, without the likelihood of spilling into public areas or into the neighbour's garden!

3. Things to check before installing a grey water system

Understanding the legal framework governing grey water use in your area is crucial. Different regions have varying regulations concerning the collection, treatment, and use of grey water, including requirements for permits and inspections to ensure public health and safety.
Selecting the right system for a household or commercial building requires a thorough assessment of their water usage, the layout of the property, and their conservation goals. For example, a simple grey water system might suffice for a small household aiming to irrigate a garden, while larger properties or those with more ambitious water reuse goals might benefit from a more complex grey water treatment system (GTS).
When establishing a grey water system:
- Make sure it can't enter swimming pools or flow into neighbouring properties
- Avoid ponding, bad smells or damage to plants.
- Keep it away from children's play areas.
- Use drip irrigation or flood watering methods to avoid the potential for inhalation.
- Avoid using grey water directly on herbs or on any plants that produce food, except trees and shrubs with edible portions that the gray water does not touch.

4. Types of grey water systems

While some types of common household “grey water systems”, such as keeping a bucket in the shower or leading a pipe from the laundry to the garden, don’t require professional plumbers, large-scale or chemical grey water systems do. Learning how to install a range of grey water systems benefits plumbing businesses hoping to target residents wanting to improve their long-term water usage management, yet don’t have the expertise to set up the systems themselves.

Simple grey water systems

These systems collect water from bathtubs, showers, and bathroom washbasins to be used for irrigation. They typically employ subsurface drip irrigation or a subsurface trench method for distributing the water.

Gravity grey water systems

Like simple grey water systems, gravity grey water systems provide a direct diversion from the feed pipe to sub-surface irrigation in the garden. They require the inlet to be higher than the outlet for gravity to work, which may result in uneven watering due to pressure issues if not installed correctly.

Pumped grey water systems

Pumped grey water systems utilise a small pump for even irrigation system performance. They often use a combination of filtration, a surge tank, a pump, and sub-surface irrigation. Different inlet sizes (50mm to 100mm) can be used to attach to a single point (such as a washing machine) or combine water from the whole household. These can be installed underground and leave a small footprint; with the largest surge tanks around 600mm in diameter. They do not accumulate water (like a rainwater tank) but distribute it efficiently.

Grey water treatment system (GTS)

Grey water treatment systems are a more complex set-up, which improves grey water quality for use in surface irrigation, toilets, and laundry. They disinfect the water through the chemical of mechanical filtration systems. The more intensive option, these systems require permits and regular servicing. Due to the improved quality of the water, they can store the disinfected water for longer than 24 hours in a second tank. However, they are also the most expensive grey water system option, with installation, servicing costs and yearly maintenance.

4. Looking to the future

The integration of grey water systems into both new and existing infrastructures shows the commitment to preserving our most precious resource: water. As technology advances and awareness grows, the role of the plumbing industry in facilitating this shift towards a more sustainable future grows. By staying informed about the latest developments in grey water recycling and advocating for its benefits, plumbing professionals can lead the charge towards a more sustainable and water-efficient future.

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