Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: thedoc on 06/03/2012 15:18:37

Title: Could we use grey water to water the crops in our garden?
Post by: thedoc on 06/03/2012 15:18:37
Is it safe to use grey water, water from the sink or from the shower et cetera, to water things like fruit trees or crops in your garden?
Asked by Steve Gale, Facebook

                                        Visit the webpage for the podcast in which this question is answered. (


Title: Could we use grey water to water the crops in our garden?
Post by: thedoc on 06/03/2012 15:18:37
We answered this question on the show...

David -   Yes.  I think I would be perfectly happy to water my flowerbeds with gray water but I think I would be just a little bit cautious about watering fruit or vegetables that you were going to eat, just as a precautionary measure.
Ben -   So what sorts of problems could you actually build up in there?  Is it going to fill up with pathogenic bacteria or is it purely just a case of, ďWe know itís been used, we know itís got the chemicals in it from say, your shampoo, and they may impact on the soil quality".
David -   Itís both of those.  I mean, there's the shampoo chemicals that might be taken up by the plant and certainly, even though this grey water comes from maybe the sink, it can also come from the shower and the bath. That can also have pathogenic bacteria in it.
Ben -   He also mentions another one which is the runoff the drip collected from an air-conditioning unit.  Now air-conditioning, essentially the water that comes out, is distilled water.  Is that likely to be a problem?  Presumably, itís going to be pure and clean, and really healthy water, but is it an issue to be putting distilled water on our plants?
David -   No, I don't think that's an issue but I would just be slightly cautious with air-conditioning units of any type because of the issue of legionella which can cause Legionnairesí disease in very extreme circumstances.  Now I'm not suggesting it would cause a problem in this case, but I would be cautious with that water.
Title: Re: Could we use grey water to water the crops in our garden?
Post by: CliffordK on 06/03/2012 18:08:42
Keep in mind that there is a difference between personal home systems, and public systems.

You've already been exposed to most of the germs in your home, at least to some extent.  Ordinary soap would actually work as a fertilizer, although perhaps your shampoo has more chemicals in it.

You're probably right though, it might be best to just use the grey water in an ornamental garden.  I assume there is a fine balance with the sanitary sewage, not to have too much, and not to have too little liquid. 

Some people also construct some water gardens for their gutter runoff. 
Title: Re: Could we use grey water to water the crops in our garden?
Post by: Don_1 on 07/03/2012 15:05:17
It may not be simply a case of damaging your soil. There are a great many chemicals used in many household cleaning products and personal hygiene products. There are also those home hair colouring products, some of which contain peroxides.

A build-up of this concoction of chemicals may not just damage your plants, flowers, fruits and vegetables, it could also put ground water at risk of contamination. So I think we should be very careful of just what is in used water before we tip it on our gardens. It may be that that bowl of water is harmless enough, but what about the previous or next bowl of water, will the combination of chemicals prove to be dangerous?

Don't forget the insects living in the soil too. Many of them play an important role in soil health. Making your soil a 'no go' area for worms can also damage your soil. Which brings me to the birds which may be feeding on seeds and insects in your garden.........

I could go on, and on and on and on (I usually do, much to the annoyance of one and all), but on this occasion, I'll shut up, for a change.
Title: Re: Could we use grey water to water the crops in our garden?
Post by: Donnah on 09/03/2012 05:21:11
You bring up some very good points, Don_1, and it makes me wonder why we would use these products on our bodies and  "clean" our homes with them if they are toxic.  It makes sense to me to use only products that would be safe for a grey water system.
Title: None
Post by: greenman on 20/03/2012 12:38:38
I work as a salesman for a company that manufactures an electronic capacitor based water treatment system that is used in cooling towers, chillers, evaporative coolers and heat exchangers to control scale, bio fouling and corrosion. By keeping bacteria levels extremely low there is no slime in the system for the growth of legionella, as legionella does not manufacture the slime but needs it to grow. We can eliminate the use of chemicals within the above systems which would traditionally be used to control scale, bio fouling etc. That being said, we are able to reuse the non-chemically treated discharge water for irrigation. Can this discharge water be safely used for food crops? Will this have a negative effect on my septic tank and the bacteria if this is connected to the water line coming into the house?
It has been shown our product will reduce water surface tension by 20 to 25%, allowing for better  saturation into the soil, better nutrient uptake by the roots and allowing the salts to permeate into the soil away from the root zone, all allowing for documented higher crop yields.  I have been told the unit will keep the nutrients from settling out of solution for a period of up to 2 weeks in city water, 2 to 4 weeks in well water. Will this allow for a longer time between changes of nutrient solution in my hydroponics system reservoir, due to a longer period of time of nutrients staying in dispersion?