At the moment all the fresh drinking water we use to shower in and to do our laundry is going straight down the drain after a single use. On top of that, most of us are using more fresh drinking water to water our gardens.

This is a shame - because treating greywater on a neighbourhood scale is pretty straightforward - in principle at least.

Here's a plan showing a possible integrated blackwater, greywater and stormwater treatment system. I’ll run over the possibilities for greywater now, and cover blackwater and stormwater in later posts.

There's a lot of greywater capturing & storage devices out there which individual households can use for their own gardens. Because the greywater isn't processed, each household would have to manage their choice of laundry and toiletry products so that the water was suitable for their garden, or else use the unprocessed greywater on ornament plants which are tolerant of the salts and chemicals it contains. Subsurface delivery systems are recommended (less health risk).

But if we think on a larger scale we can do a lot more with our greywater. We could divert the water we use for washing from entering the main sewerage system and have it carried from our laundry and showers by underground pipes to a series of reed beds housed in a greenhouse located in the existing community garden area.

This reed bed will be capable of processing our greywater, regardless of products used in it, to a level where it is safe for use on all plants (including edible plants). Strictly speaking it would be potable, but the recommendation is that you use this kind of water for everything except drinking.

This wouldn't be a cheap intervention, and I imagine the main cost would be in upgrading the existing sewage infrastructure. Of course it depends on who is paying the bill. If we cover the cost as residents, then it will probably take a long time before it pays for itself (assuming water stays as cheap as it is) - but if state government decided to invest in the local treatment and recycling of our water then it would have the benefit of helping to relieve the pressure and cost of maintaining and upgrading our major centralised infrastructure, and maybe then it's not such a bad deal.

In terms of infrastucture the most complicated aspect would probably be setting up the plumbing to capture the greywater in individual houses - some houses in our neighbourhood have suspended timber floors and would be pretty straightforward, but others would be quite difficult. Digging down to the existing sewage and running an greywater pipe alongside wouldn't be technically difficult, but would require a significant amount of earth works.

So what are the benefits of having a greywater treatment system? Well, we'd reduce the amount of drinking water we use for watering the garden (and possibly, for flushing our toilets) which would in turn reduce the pressure on the existing infrastructure, and it would be easier to keep our gardens and street tree's alive in summer. And we'd also reduce the amount of water entering the sewage system, with flow on benefits to existing treatment systems, and the amount of water entering the bay.