[Paul Anderson]

Paul Anderson  asked the Naked Scientists:
   
Hi Chris and team,

Could you comment on grey water?

I run the water from the clothes washing machine out the window and into a coupld of galvanised iron rubbish bins. Then I rush outside and cart buckets of grey water around to my trees. I get exercise that way.

Is grey water bad for vegetable gardens? Is it bad for trees? When I had young sons I used to use the nappisan water from the nappies to tip around the feijoa bushes and I am sure we had good feasts of feijoas then. The soap powder is supposed to be biodegradable. I suppose I should type in all the contents on the side of the packet.

My father used to say that dog droppings were no good for the garden because they were carnivorous. My brother-in-law used elephant droppings but then they are vegetarian.

Regards
Paul
NZ

What do you think?

[Mazurka]

I have used a very mild soap solution as a pest control spray - seems to work agsint aphids, mealybugs, whitefly and ants.

[Karsten]

Gray water by definition is what runs down your shower or bathroom sink drain. Possibly also the kitchen drain. It may basically mean that it is all the waste water that does not include the toilet waste or kitchen waste.

Anyhow, there is nothing said about what cannot be in gray water. If you choose to dump dangerous chemicals down your drain, well, it may not do your trees much good. If what goes down any drain is good for the garden, it will be good for the garden. Does not matter which drain or which "color". In some cases it might be better water after it has been treated by microorganisms in the ground.

I would stay away from putting dog feces on vegetables for human consumption unless it was composted at high temperatures for a year or longer.

[litespeed]

I agree with Karsten

By definition gray water is any discharge that does not include human waste. As you point out, much of it consists of laundry discharge. This includes substantial amounts of various fertilizer type nitrates. Anyway, as long as the gray watter does not include poisons dumped down the kitchen sink for one reason or another, I suspect it is a fine method to water/fertilize agricultural production.

Further, to this day, human waste is used to fertilize agricultural production in numerous third world sorts of places. The produce [such as green onions and lettuce] is safe enough, but needs to be submerged in dilute Chlorine (chlorox) solution to kill collateral pathogens. I have done it, but don't recommend it.