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Shades of grey

July 17, 2016

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So does this geranium
So does this geranium

The suggested use of grey water for plant irrigation seems to have sent some readers into a tizzy of confusion; therefore, this week, we will take a look at exactly what grey water is and the easiest way to use it for plant irrigation.

Quite simply, grey water is the term used for water which has already been used for things such as showers / hand washing, laundry purposes, washing vegetables and even from washing the dishes.

This water generally disappears straight down the drain into the sewage system but is, as long as guidelines given below are followed, perfectly safe for garden use.


If basic guidelines are followed, grey water is perfectly suitable for the irrigation of indoor and outdoor plants


Grey water is good: ‘Black water’ from toilets and from chores such as washing / cleaning anything or any area which may be contaminated with human waste is not safe for garden use, unless it has been professionally recycled through an approved sewage treatment system.

Ensuring that household grey water is suitable for irrigation does, however, take some effort on the part of absolutely everyone, including domestic help, who may use tap water for whatever purpose; the use of some commonly used substances must be avoided with a switch over being made to more acceptable, environmentally-friendly, alternatives.

To be avoided:

  • Bleach, chlorine based cleaning products, acid / alkaline cleansers, sodium salts, solvents and any product containing boron as all of these are toxic to plants and can also, over time, cause long-term damage to the soil.

  • Bath salts, chemical dyes such as for colouring hair, shampoos, conditioners, ‘regular’ soaps and other beauty products that are easily available in the market, are quite liable to contain ingredients that are harmful to plants and soil. Reading the list of ingredients before purchasing / using any of these items is a must if recycling grey water is what you intend to do.

The above, at first glance, may put you off but consider the fact that in reality, each and every one of the items listed can be replaced with a more natural alternative, the use of which is far better for human beings too.

Take cleaning materials for instance: potentially toxic cleaning materials are an obvious danger to human health via skin contact, via accidental inhalation and so on and so forth. Switching over to the use of clearly labelled, genuine, environmentally-friendly cleaning products makes good sense.

This ‘Wisteria’ thrives on it
This ‘Wisteria’ thrives on it

It is actually possible to make many, relatively low-cost, environmentally-friendly cleaning products at home and this subject is one which you may care to look in to. The same applies to beauty products including soaps, shampoos and even a wide range of natural hair dyes in addition to the usual henna.

For now though, anyone thinking of using grey water in the garden should dispose of all ‘questionable’ cleaning and beauty care products and replace them — and these can be tracked down — with items such as pure, unadulterated, laundry and hand / body soaps — soap nuts are a wonderful natural option — and don’t forget pure neem products in the household cleaning department. The switch, especially if household members are in the habit of using popular brands, may not be easy but here’s a useful bit of advice: if it isn’t safe to eat / drink, putting it on hair / skin — from where it is eventually absorbed into the blood stream — isn’t a sensible thing to do!

Dish-washing water, especially when traditional food is on the menu, is bound to contain a certain amount of oily residue. This can easily be strained out, to a tolerable degree, by pouring the dish-water through a simple filter such as a reusable (after washing) piece of fine cloth suspended / fixed over a large bucket, the resultant cleaner water then can be used in the garden. An alternative to this form of filtering, is to use the ‘matka irrigation system’ (more on this another time), pouring the used dish-washing water directly into previously emplaced matkhas from where it will be filtered out as the water seeps through the unfired clay into the soil around it. Residual build-up should be scrapped out of the matka as necessary.

For reasons of hygiene, it is recommended that grey water does not come into direct contact with plant leaves or with fruit / vegetable skins. This is not alarmist, merely a case of ‘better safe than sorry’.

Grown with grey water
Grown with grey water

The easiest way of recycling grey water is by the bucketful, directly out into the garden for same day use: it should not be stored for more than 24 hours or else it will begin to smell, and unless tightly covered, provide a breeding ground for mosquitoes.

Do not panic if the grey water contains small amounts of food residue — the emphasis being firmly on ‘small’ — as this provides extra nourishment for plants.

It is possible to have purpose-built grey water collection systems installed in your house. These involve the installation of separate drainage pipes into an outdoor storage tank and I personally know of householders in Karachi who have had this done with excellent results on the gardening and water / cash saving fronts.

There have been many scientific studies over the years and in various parts of the world; all have proven that grey water is, providing basic guidelines are followed, perfectly suitable for the irrigation of indoor and outdoor plants — be these plants edible or otherwise.

Please continue sending your gardening queries to zahrahnasir@hotmail.com. Remember to include your location.

The writer does not respond directly by email. Emails with attachments will not be opened.

Published in Dawn, Sunday Magazine, July 17th, 2016