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How Greywater Systems Work, The black and white about greywater

Greywater is a very often a forgotten resource,  in this article, we’ll look into what exactly is greywater, how greywater systems work and the benefits of reusing greywater.

Drought is not something typically associated with Canada. Yet long droughts (like those we experienced in the early 2000s) have been among Canada’s costliest natural disasters – particularly affecting southern regions in British Columbia and the Canadian Prairies.


Water is an incredibly important resource across an enormous range of sectors, from agriculture and manufacturing to recreation, ecosystems and human survival. It’s one of those cases, where you really “don’t know what you got till it’s gone”.

benefits of greywater systems

So – what is greywater?

Greywater is used in household water from baths, showers, bathroom basins and washing machines. It’s important to note that this does not include the waste that’s flushed down the toilet or dishwater drained from the kitchen sink.

greywater system

Greywater can be used for low-risk purposes, for instance, toilet flushing and the subsurface irrigation of lawns or gardens.

How is greywater different from sewage?

There’s Blackwater and there’s greywater: both are types of wastewater.

Greywater, as we’ve just read, results from inorganic household activities like having a shower or doing the laundry. Blackwater, on the other hand, is wastewater that contains organic matter like the bodily waste we flush down the toilet or the scraps of food that may end up down the kitchen drain.

re-using laundry water

Greywater can be easily recycled because it contains a lot fewer bacteria and pathogens than blackwater. Understandably, the treatment needed to kill the disease-carrying bacteria present in Blackwater is much more intense.

What are the benefits of a greywater recycling system?

As global access to water currently stands: two-thirds of people worldwide have to live through at least one month of severe water scarcity each year and half a billion people face water shortages all year round.

water recycling

Water itself is not a scarce resource. More than 70 per cent of the earth’s surface is covered by water, from seas and oceans to rivers, snowfields and glaciers. But only 2.5 per cent of this is fresh; the majority is saline and ocean-based. And even then, only about 1 percent of the earth’s freshwater is easily accessible – with much of it being trapped in glaciers and layering mountaintops as snow.

When you have a shower, you use anywhere between 9 and 20 litres of water every minute. One washing machine cycle uses about 150 litres. Typically, 50 to 80 percent of a household’s used water is greywater. So capturing this greywater and recycling it can massively reduce a household’s overall water consumption.

greywater system

In fact, the benefits of recycling greywater are numerous:

A reduced demand for freshwater: A single flush of a toilet uses between 6 and 13 litres of water. By using greywater to flush the toilet, instead of freshwater, a household’s demand for freshwater can be significantly reduced. Not to mention watering the garden: in warm weather, almost half of the water consumed by the average North American household is used outdoors. Capturing greywater from indoor activities to use outdoors can help reduce water consumption.

Plant growth: Greywater can help plants grow in areas where there may not naturally be enough rainwater or freshwater to support plant life. Additionally, when greywater seeps into the soil, bacteria living in the soil break it down into nutrients on which plants can feed. This boost to soil fertility is another win for plant life.

Replenished groundwater: When used for irrigation, recycled greywater replenishes groundwater, urging on the natural water cycle.

greywater re-use

Development of otherwise unsuitable land: As mentioned in our previous article about Above Ground Septic Systems, certain environmental conditions can make a traditional septic system impossible to install. (For instance, when the water table is too high or when there is not enough topsoil under which to house the system).

By reducing the amount of water that needs to be discharged from a septic system, a greywater recycling system can ease the struggles of installing a septic system on land with shallow topsoil or insufficient space.

septic system for cabin

Less pressure on septic treatment systems: Because greywater makes up the bulk of a household’s wastewater, diverting greywater from the household septic system extends the system’s life and capacity.

From pipes to plants: how does a greywater system work?

So the benefits of recycling greywater are many. However, greywater can only be safely recycled using the right mechanisms and processes. At GroundStone Wastewater Services, we have a specially selected range of greywater systems for homes and businesses. Here’s how they work:

Collection: Used household water from baths, showers, bathroom basins and the laundry is diverted into dedicated greywater stack piping. (Water from the kitchen sink is not recommended for recycling because of the potentially high levels of organic matter like oils, fats and scaps of food). The greywater makes its way through the stack piping into the tank, which will usually be underground.

greywater septic system

Pre-filter: Once inside the tank, the greywater passes through a pre-filter, which removes any hair or other large particles so that only water moves on into the tank chamber. A tank overflow drain gets rid of these particles and any excess water.

Disinfection chamber: Free of unwanted particles, the greywater finds its way into the tank chamber, where it is disinfected – typically by the virus-eliminating properties of bromine. The water moves over bromine tablets, to an activated carbon filter.

Activated carbon filter: This removes discolouration, any tiny particles that made it through the pre-filter and excess bromine. From here, the water is pumped to the roof header tank.

Pumping: The roof header tank is where gravity takes over. From here, the now treated greywater flows to where it’s needed. If it so happens that there isn’t enough treated greywater available, a mechanical ball valve in the header tank automatically tops the system up with mains water, ensuring a continuous supply.

Recycling greywater: some caution

Freshly collected greywater is much less difficult to treat and recycle than blackwater, but only if the greywater is handled properly. If you have a greywater recycling system or are considering getting one installed, it’s important for you to be aware of several factors.

For instance, there are the potential environmental impacts of putting greywater to use. Some aspects of greywater system maintenance and household activities (say, using harsh cleaning products and laundry detergents) can make the greywater particularly chemical-potent. Consequently, it is important to have your greywater system positioned and working in such a way that there isn’t any runoff.

Then there’s the fact that greywater decomposes at a much faster rate than blackwater. Storing greywater for even as little as 24 hours can make it a playground for bacteria, which use up all the oxygen. Without oxygen, the greywater will become anaerobic and then septic. When this happens, the greywater becomes more like Blackwater, which (depending on your septic system and property size) cannot be recycled as easily or at all.

The effectiveness of a greywater recycling system also depends very much on site-specific factors like the property size, soil composition and the actual placement of the system. So it’s important to assess how the system will be used before it is installed. A greywater systems expert will be able to lead you through this assessment and advise on the best placement of your system.

Do any laws apply to the use of greywater?

Under the Sewerage System Regulation, greywater is technically considered sewage.  Discharging greywater onto land or into a source of drinking water, surface water or tidal waters is considered a health hazard.

All domestic sewage originating from a building “must go into a public sewer or a sewerage system, unless it is authorised under the 2012 Building Code” the regulations state. The 2012 Building Code allows the construction of non-potable (not of drinking quality) water systems, and subsurface irrigation with non-potable water.

The Health Canada Guidelines for Domestic Reclaimed Water for use in Toilet and Urinal Flushing provides further guidance for greywater systems.

The Future of Greywater

Greywater recycling systems are here to stay. Leaders across the country are working furiously to integrate this new option into codes and policies to offer clear guidance for users. Future developments in policy will include guidance and policy on treatment strategies, cross-connection protections and rainwater harvesting. Some of these aspects are already being developed into some Provinces’ policies. Provincial leaders on the topic include British Columbia, Alberta, Manitoba, Ontario and New Brunswick.

Our maintenance experts at GroundStone Wastewater Services are up-to-date with all of these legalities and will be able to advise whether a greywater recycling system is right for you and your home.

For a quote specific to your location and situation, call 250-768-0056 to speak with one of our maintenance experts.

Luis Goncalves, ROWP, IN, PL

I fell into this amazing trade quite by accident, I have always loved being around heavy machinery and moving earth and in contrast love working with designing things.  This trade in the septic field has led me down a wonderful path of exploring all of my skills and passions while working hard at achieving success.

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