When it comes to household wastewater, two terms come up again and again: greywater and blackwater. Not the most glamorous topic, admittedly, but an important one.
Greywater is wastewater from household plumbing other than a toilet. This includes water from showers, bathtubs, bathroom sinks, and laundry. In some areas, kitchen sinks and dishwashers are included as well.
Blackwater is wastewater from toilets and contains feces, urine, and other bodily waste.
How does greywater differ from blackwater?
The simplest way to think about it is this: greywater comes from everyday washing and cleaning, while blackwater comes from toilets.
That difference matters because the rules for handling and disposing of each are not the same. Local governments may also have bylaws or other rules that allow the surface discharge of greywater if it meets applicable building code requirements.
Depending on where you live, greywater can include kitchen wastewater, while in other areas kitchen wastewater is treated differently. The best practice is to check with your local authority to confirm the bylaws or other rules that apply to greywater disposal, including whether surface discharge is allowed and under what conditions.
EcoEthic is based in Ontario, where greywater leaching pits fall under Class 2 leaching pit guidelines. In that guidance, leaching pits are used to treat and disperse greywater sewage only and are not to be used to dispose of toilet water. These systems are also intended for smaller volumes, with a maximum daily flow of 1,000 litres.
An important note about composting toilets
This is where it can get a little confusing — and a little messy.
Some composting toilet manufacturers have directed customers to drain overflow liquid into a greywater pit. Based on the Ontario guidance above, that does not align with how a Class 2 greywater system is intended to be used. These systems are for greywater only, not toilet water.
So if you have a composting toilet with a drain, or are considering one, it is important to know that directing toilet liquid — whether straight urine or mixed liquid — into a greywater pit or leaching pit is not allowed.
If you’re not sure what applies in your area, please check with your local health department or building department for the facts.
Greywater systems still need care
Greywater is different from blackwater, but it is not just clean water.
As greywater percolates through the layers of a leaching pit, the upper layer of soil filters out solids, while naturally occurring bacteria continue the treatment process below the surface.
When that balance is disrupted or overburdened, performance issues usually follow. Slower drainage and odour are often early signs that organic material is building up faster than it is breaking down.
Adding targeted microbes helps support that natural process and keep the system working the way it should. EcoEthic BioSurge for Outhouse or EcoEthic Septic System and Drain Treatment both contain targeted microbial formulas to help bio-augment a greywater system, support the breakdown of organic material, reduce odour, and improve flow.