Jump to content
Science Forums

Grey water


Recommended Posts

This Guy is not getting the info he needs.


Any good chemists out there that can give him the good gen??



PostPosted: Wed Aug 30, 2006 5:17 am Post subject: Using

laundry greywater

We are using laundry greywater for veggies and trees.

We should perhaps build a filter like mentioned in another thread, but first we should avoid the false laundry powders.

I read that sodium an phosphate are the ingredients which are bad for the soil. With phosphate it is simple because it is marked on the box, but how do I find out the sodium level?Are there sheets with brands and ingredients?

Is sodium (cooking salt?) necessary for laundry and are there powders without sodium? Or should we all write to our supermarkets demanding what is in the laundry powder?

Link to comment
Share on other sites

Well, I'm not a great chemist but AFAIK the trouble with the phosphates in detergent is that they fertilize, which is an eco-problem in rivers because it causes excessive vegetation. It shouldn't be a problem for the trees and veggies that you want to grow as much as possible...


As for the sodium, there may be a reasonable way to precipitate at least some of it out.

Link to comment
Share on other sites

All sodium salts are soluble in water, so you wouldn't be able to precipitate it out. Adding a lot of sodium to the soil would, of course, make it saline, and fertilisers and other chemical agents have no effect. You have to leach the salts out of the soil. I'm pretty sure all detergents are sodium salts, so that would be one of the big problems with using grey water.


The nitrates and phosphates need to be largely removed. Using too much of any fertiliser will have a negative effect on your garden. Phosphates don't have much of an effect on the pH of the soil, but nitrates will lower the pH and burn your plants. Q is right about the phosphates and nitrates contributing to cultural eutrophication in water sources, too. If the vegetable patch is near a fishpond or something like that, you'd run the risk of killing your fishies off with an algae plague.


That guy really should get a filter and something to treat the water, especially if he's eating the vegetables raw. I assume he's just watering his garden with the grey water, as opposed to having a submerged irrigation system. The water should really be treated with chlorine to kill bacteria, and the phosphates can be precipitated with calcium compounds, I'm sure.

Link to comment
Share on other sites

  • 2 weeks later...

I am going to have to start to use greywater myself soon.

Local dams are down to 14% and 97% of the State (NSW) is drought declared.

I have discovered there are some eco-friendly washing machine detergents. I assume they are low in phosphates and nitrogen. Australian natives hate phosphates as a rule.

I can't see that there will be much of a problem with my bathwater because there is so little soap in it. In fact it might act as a wetting agent (?) but the washing machine might cause problems but it will be going on to lawn and a few camellias.

Many Local Council regulations proscribe the uses of grey water. I am not sure why, but it does scare people off using it.(Especially in the veggie garden??)

Link to comment
Share on other sites

I am going to have to start to use greywater myself soon.

Many Local Council regulations proscribe the uses of grey water. I am not sure why, but it does scare people off using it.(Especially in the veggie garden??)


I propose a simple solution is to build a small greenhouse distiller. With the floor a water-tight tray, the gray water is poured in. Clear plastic walls and roof set on angles collect the condensed water & direct it to gutters which direct the now fresh water to a collection vessel. As salts etc. collect in the tray it is periodically collected & disposed of in the regulatory fashion.:QuestionM

Link to comment
Share on other sites

I propose a simple solution is to build a small greenhouse distiller. With the floor a water-tight tray, the gray water is poured in. Clear plastic walls and roof set on angles collect the condensed water & direct it to gutters which direct the now fresh water to a collection vessel. As salts etc. collect in the tray it is periodically collected & disposed of in the regulatory fashion.:beer:

Good suggestion-a simple solar still. That would get rid of the salt.

Would it also get rid of detergent/soap do you think?

Link to comment
Share on other sites

Yep; it's just evaporating the water out and condensing it elsewhere, leaving the solutes in the tray. Natural soaps are just sodium or potassium salts of fatty acids, and laundry detergents, dishwashing liquids and powders are sodium salts of a long chain alkylbenzene sulfonate. Hair conditioners are just quaternary ammonium salts- a nitrogen atom bonded to four carbon chains, and positively charged. Remove the water and you're left with the solid salts.

Link to comment
Share on other sites

Thanks igby

There is alot of chemistry in soap!

I found this site


Choosing greywater-compatible soaps and detergents


Cleaning products labeled “biodegradable” or “natural” or even “eco-friendly” may not be garden-friendly or “biocompatible” — suitable for the plants and soils of your greywater-irrigated landscape.


According to State of California Department of Water Resource’s Graywater Guide: Using Graywater in Your Landscape [2], specific ingredients to avoid include:


-chlorine or bleach


-sodium perborate

-sodium trypochlorite



-petroleum distillate




-”enzymatic” components


Two common ingredients in synthetic detergents and soaps (including homemade kinds) are sodium and boron. High levels of sodium and other salts in soil are a special concern in arid areas where soils tend to be high in salts already. Salts can raise the alkalinity of soil, degrade the structure of soil, and harm plants.

To prevent a buildup of salts in garden soil, minimize your use of soaps and detergents that are made with sodium compounds.

Avoid powdered soaps and detergents especially, because in addition to normal amounts of sodium used, they include “filler” ingredients that usually are high in sodium.

Link to comment
Share on other sites

  • 1 month later...
Just curious, but doesn't bathwater constitute a possible e-coli threat if used for food crop irrigation in warm climates?



Most garden programmes I have been watching have suggested not using grey water on vegetables. Perhaps this is the reason?

I use a big spar so I find it hard to believe such water can be a problem. But I have been using (recycling) it on my ornamentals; as Australia is now in the grip of the worst drought in its European history.


I found this link hard to understand but it may be relevant


Link to comment
Share on other sites

Methinks that link is about a chemical for use in sewer treatment plants for cities etc.. ;)


I found a couple of links that address the gray water issue. For the most part it seems discouraged, but may be used with proper caution if not prohibited by local health codes (apparently it's illegal in Washington State, USA).





Some excerpts from the top link: "Recycled water from the bath, shower, or washing machine could contain organisms causing diseases in humans. However, when gray water is poured onto soil that has an abundance of organic matter, the potentially harmful bacteria and viruses die quickly...


...Do not recycle water from a washing machine that has been used to wash baby diapers because it may contain fecal matter....


...Do not apply gray water to leafy vegetables or root crops....


...Apply the gray water directly to the soil surface. Do not use an overhead sprinkler, or allow the recycled water to splash off the soil and contact the above-ground portion of the plants...."



Link to comment
Share on other sites

  • 6 months later...

This is a commercial site full of adds for their products but it does have some useful info.

This is a little grey-water diverter they sell

Green Garden-Grey Water

It does seem a bit small, only holds 110 litres


But the bigger units I have looked at have to have a plumber, council planning permission, an aerator pump (running on on and off- must cost a bit in electricity), a pressure pump and a huge storage huge tank. Sounds like you have to have a big garden or be fairly committed to go though that process.

I hate pumps. When I had a nursery I was always getting my submersible bore pump fixed.


I just siphon my bath water out with a big piece of polly pipe.(I found it under the house fortunately, as I priced it at the hardware store and it is VERY expensive)

I find one bath full (I fill the bath with me in it) waters about 100 pot-plants, of varying sizes, I have now accumulated.


Here is a blurb on grey water at the same site

Green Garden-Grey Water

Sydney Water estimates that an average household (3.5 people) produces 586 litres of wastewater each day.

How much wastewater can be used as grey water?

Approximately 61 per cent of the total wastewater produced by an average household can be used as grey water. Kitchen wastewater is not usually included in this amount. The table below indicates the total amount of wastewater and grey water produced in your home

So about 300 litres a day is a lot of water to be throwing away.:turtle:


I am beginning to think that the main problem with detergents etc is salt and pH.

I can't see how phosphorus (it is a fertiliser after all) would be a problem except with some Australian native plants who don't like too much of it.

I am not sure how much salt detergents contain (if any). I have not seen any detergents tell you waht pH they are on the bottle.

Sydney has soft water and so salt is not necessary. I did notice when buying a dishwasher that some German-made models had a place to put in a cup-full of salt. The salesperson told me that this was because water in Germany was "hard" (whatever that means). But most grey-water systems don't use kitchen water So. . ?


The same site sells a detergent (pH neutral) that they have put fertiliser in! Clever.

It does seem very expensive. But you never know with detergents what is really expensive or not because it depends on how much it has been watered down.

Anyone used it?

Green Garden-Grey Water


If you are interested their home page has a list of all the water restrictions in Oz capital cities. In the countryside things are often much grimmer.

'They' are talking about having problems producing electricity from hydro soon.

Green Garden-Grey Water

Link to comment
Share on other sites

  • 5 months later...
  • 1 month later...

I have been doing alot of clothes washing this week as the washing machine has been broken for two weeks. All the waste water has been going to the garden. I have used two large bottles of detergent.

I have been using "Hurricane Plant Green" detergent(NO phosphorus -but no other information) and thought I'd better check on its salt content so I sent a letter to the manufacturer. This was their reply:-

Colgate-Palmolive recommend consumers who wish to recycle the grey water

from their washing machine follow the information below.



* Consult your local water authority to ensure they will permit you to use

untreated grey water;

* Only use the rinse water from your machine, not wash water, due to the

alkalinity of the wash water;

* Rotate the area you apply the grey water to;

* Carefully monitor the areas the grey water is used on and stop if any

issues occur;



* Do not use the rinse water if it contains fabric softener;

* Do not use the rinse water from soiled washloads containing bodily


* Do not use the grey water on new plants, vegetable gardens or green leaf



Please note that while this information is provided in good faith, our

products have not been formulated with this use in mind and have not been

tested for this application.


Hurricane Laundry Liquid contains less than 20g of sodium per wash.


Thank you for taking the time to contact us. We hope this information is



Yours sincerely


Anna Truong

Senior Consumer Affairs Representative


20 grams in EVERY capful !! O no. I wonder what will survive!

That expensive detergent I mentioned before doesn't sound so expensive now.

Link to comment
Share on other sites

  • 2 months later...

It's not easy beeing green.

(radio transcript)

. . .

This product says it has a low salt content, and is greywater safe. But Professor Selinger says it contains boron compounds, which could pose a risk to your garden.


Ben Selinger: In fact there's a CSIRO soil expert I talked to killed his own garden re-using the washing liquid which had boron in it, which he should have known better. So there are some subtle compositional issues there. But products which say they're safe to use on the garden have to be low in sodium and not have any borax in them.

To summarise, the specialist green brand had salt in it, the supermarket green brand had a chemical in it that could kill your plants.

And finally, the difference between the supermarket brand advertising itself as green, and its standard competitor that makes no environmental claims, is negligible.

. . .

Rachel Carbonell: Of all the products that we've looked at so far, there aren't any actual lies being told. But the marketing can be distracting, and at times a little disingenuous.

. . .

Scott McDougall: We found over a thousand products across these six stores, we found over a thousand products that collectively made over 1700 environmental claims, and found that almost all of them, 99% were at risk of either being false or of misleading their intended audience, and we sorted those misleading claims into patterns, which we've come to call the 'Six Sins of Greenwashing.'


Rachel Carbonell: The Six Sins of Greenwashing are: the sin of the hidden trade-off; the sin of no proof; the sin of vagueness; the sin of irrelevance; the sin of the lesser of two evils; and the sin of fibbing. We'll go into more detail about some of the more common so-called sins, shortly.


But one of the most telling revelations to come out of the Six Sins of Greenwashing, was that the sin of fibbing, or actually telling outright porkies, is the least common

Background Briefing - 10 February 2008 - Greenwashing

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...