Greywater reuse

The Reef
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I recently stumbled upon greywater reuse twice:

  1. Apparently companies that offer recycling showers also offer greywater reuse

  2. In an old technical document from the JRC (p. 19)

For clarity: greywater is the wastewater that comes out of the sink, shower, bathtub and washing machine (so everything except the toilet).

It intrigues me because this is one of the few features that they have in Schoonship but not us. It also interests me, because a quick back-of-the-envelope calculation might point out that in a period of extreme drought, we might not have enough rainwater in stock to guarantee flushing the toilets.

So if anybody would feel inspired, I think it could be worth looking into whether it would be meaningful to provide for the right piping - i.e. separate collection and the possibility for supplying the toilets - without necessarily already investing in the reuse technology itself (= filtering and pumping).

As a small side note for our own records: I know one of the authors of the report linked above, so just in case it might be interesting one day I could ask whether he would be open for a short chat with one of us.

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Water use at home: how much do we use for wat?
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I read this is not so straightforward.
I wouldn’t mind going talking to sb of cohousing Jean. They have installed a system to recuperate grey water.
I also read they have a water expert in the cohousing and they have received financial support from VLAIO, so i guess they won’t mind spreading their knowledge to another cohousing.
If somebody would be interested in joining, let me know…

Article in dutch: Recuperating grey water: first showering, then flushing

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Fantastic! I’m super interested and I would love to join if possible.

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There is also a ‘facilitateur eau’ at l’ibge, but only for professionals and I see their focus is on rain water.

There was a presentation about the reuse of greywater (with a representative of GEP, the same that installed the greywater reuse installation in cohousing Jean) in 2025.
Link to the presentation
Link to the Q&A

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A meeting scheduled with Cohousing Jean on Monday 21/09 at 14:00.

If somebody else want to join, feel free.

Fyi:

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For those interested, here is a small report of the meeting @Lee and myself had with Bart from cohousing Jean about greywater reuse (/captation and use of rainwater).

A bit of background of cohousing Jean

They are a cohousing of 10 families (9 3BR’s with mainly 4 inhabitants, and 1 studio).

They bought a building that they completely demolished and build new units.

They were one of the pioneers to have installed a greywater recuperation system (for households), so not a lot was known at the time they did their installation.

Their technical setup

They installed a reservoir of 10 m3 to recuperate rainwater.

They have a semi intensive green roof on part of their roofs .

They have installed a greywater recuperation system of GEP, which is an underground installation, taking up little space in their basement.

They recuperate the grey water from shower (he wasn’t sure whether they recuperate the water from the sinks in the bathrooms) and they use it for flushing the toilet. The goal was also to use the recycled grey water for washing machines but the setup was done incorrectly so this is not yet the case.

Cost

More or less 30 000 euro.
700 euro/year for maintenance

What I take from the discussion (@Lee , feel free to complete)

It’s not such a straightforward/ a more complex system than eg rainwater recuperation.

You don’t do this kind of installation for financial gains, but for ideological/ecological reasons.

They don’t seem to be much restricted in their use of products when taking a shower (biodegradable shampoo’s/products,..)

Questions and answers are in this document (Team building/Sustainability/greywater reuse/questions)

PS: I will still make a more elaborate document with all the info I’ve read about greywater recuperation

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