Irrigating With Gray Water

Irrigating with gray water can be a great option for watering the garden, but keep in mind a few of these safety concerns.

| July/August 1983

  • grey water irrigation - wooden washtub
    As long as you aren't putting the water directly on edible crops, grey water irrigation is a safe and viable practice.
    Illustration by Fotolia/cmeree

  • grey water irrigation - wooden washtub

In order to save money and eat better quality food, I grow my own vegetables (as do many people these days). I recycle the “gray water,” used liquid that does not contain human waste, from our washing machine and kitchen sink by irrigating the garden with it. Is this a safe practice? I assume that, with the new “no phosphorus” soaps, this setup won't harm my plants or be dangerous to the environment.

Sounds good to me, but you need to keep a few key points in mind. First, your city, county, or state health department will likely oppose your practice, since they may confuse it with black-human waste-filled-water, which can contain pathogens that cause sickness, or even death. (If small children live nearby, you can surely expect such opposition.) Second, some gray waters do contain pathogens (bacteria and viruses) from washed diapers, underwear, and similar items. So use caution appropriate to the origins and composition of your own kitchen and laundry waters. Third, I strongly recommend against using gray water directly on edible crops, particularly on ones that will be eaten raw or slightly cooked because of the risk of contamination.

On the positive side, using household gray water for corn, grains, fruit trees, and lawns makes a lot of sense in almost any climate. Rather than broadcast or spray the liquid, though, trickle the water directly to the plant roots through a “soaker” or perforated hose.

Since phosphorus is an essential nutrient for vegetation (all commercial fertilizers contain the element), I'd recommend that you go ahead and buy phosphate-based detergents, instead of non phosphate types based on carbonate or-especially-silicate buffers. Read the package to know what you're going to be putting on your lawn and garden.

David Burmaster, consultant on surface- and ground-water quality and hazardous waste management 

Wade Mann
8/10/2011 7:24:45 PM

Continuing on from my previous comment Phosphare is absotbed into a mineral called Fluroappetite and cannot be reversed. The phosphorus you see shining in the water is actually Fluroappetite. As for drip feeders near your plants if they are not moved every now and then, the soil under your drip feeders becomes very acid. If you want to use your grey water it is a good idea to buy soap without sodium laurel sulphate in it- see above website.The toxic lauryl is spelled with a "Y" Cheers Wade WE CAN SURVIVE WITHOUT OUR MALE GODS BUT WE CANNOT SURVIVE WITHOUT OUR MOTHER EARTH

Wade Mann
8/10/2011 7:12:25 PM

The problem with using gray water in the garden is that soap is made of sodium lauryl sulphate. The sodium in soap suds actually takes over soil particles and pushes nutrients off exchange sites on soil particles and eventually ruins your soil by creating more salt in your soil and by making the soil particles separate into its lattice layers. For more information on the effects of sodium on soil go to Lauryl which is not good for your health or skin is going into the soil and becoming available gor plant uptake. Sulphate is reduced to sulphur dioxide and disappears into the atmosphere as a gas. Plants do take up sulphate but not under anaerobic conditions. If you want to know more about sodium lauryl sulphate do to this website Phosphate is not really a problem because it gets absorbed into a mineral called Fluroappetite


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