House Design

Grey Water

Grey water is made up of all the wastewater generated by a household. It includes the wastewater from your laundries and bathrooms and kitchens, and basically all your other wastewater pipes, except for those connected to your toilets; sewerage water (also known as blackwater) is its own separate thing. The difference between wastewater from toilets and grey water, is that grey water can be stored and reused on your property. This reduces your overall water consumption, and can come in handy in drought situations, especially if water restrictions are in place.

Not grey water. No matter how clean it looks…

Grey water can’t just be used anywhere on your property. You can’t use it to bathe, and you definitely can’t use it as drinking water. Typically, grey water is used to water gardens or to flush toilets. That doesn’t sound like a lot of uses, but both the garden and toilet are responsible for a high percentage of your household water usage.

Because of potential health effects from grey water (it’s not great to come into physical contact with it), depending on where you live, you may need council approval to set up a grey water system. If you are allowed, then it’s imperative your grey water system is properly installed and maintained. The way it works is by sending your wastewater to a surge tank.

A simple, laundry water surge tank

This tank temporarily holds the water before diverting it to an irrigation or treatment system. The irrigation system waters your garden, and the treatment system funnels the water to your toilets for flushing. It’s important that the surge tank is routinely emptied as greywater cannot sit for an extended amount of time. In the event that there is not enough fall to easily drain water into the surge tank, then a pumped system will be required. Any excess grey water needs to overflow into the sewerage water system.

If you’re intending to use grey water on your garden, you should note that there are certain restrictions that should be observed. Grey water needs to be kept away from  human contact, and as such, any grey water used on the garden needs to be irrigated beneath the ground.

Caution is required regarding above ground, grey water irrigation

Similarly, grey water should not be used on plants that are intended to be eaten. Grey water for flushing the toilet will require the services of an experienced plumber to set up and, because of the pipes required, maybe be difficult to achieve with certain kinds of floor systems if retrofitting.

Once you have a grey water system installed, you’ll need to be mindful of your wastewater in several ways. You’ll need to be careful about the types of soaps and detergents you use, especially if using your grey water on the garden, as you could unintentionally harm your plants. You’ll also need to be aware of any pooling of grey water in the garden, as this can lead to the build-up of harmful microbes in the soil. Water from kitchen sinks can also be problematic because of the bacteria that can come from meat scraps. As such, it is important to remember that whatever is poured down your sinks and drains will inevitably be processed through the grey water system. Because of this,
your system should include the option to divert grey water into the sewerage system; efficient filters will also need to be attached to the surge tank, which will require regular checks and cleaning.

A sketch of a grey water filter system

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