uncomposted animal manures be applied at least 90 days prior to harvest for crops whose edible portions do not come in contact with the soil and at least 120 days prior to harvest of crops whose edible portions do come in contact with the soil.
If those are the recommended intervals for manure (concentrated black water?), perhaps another question might be how long of interval should there be between grey water irrigation and harvest?... Of course, it would probably also depend on what is in the grey water.
Provided no strange chemicals are going into the greywater, I wouldn't worry much. Bacteria, etc. do not translocate into and through the vascular system of plants (unlike chemicals, which can and do!). So the only danger is from direct contact with the greywater-impregnated soil, or by soil splash from rain or watering. This is the same sort of thinking governing food crops and humanure. Tall plants which produce their yield well above ground are by default safer, as are food products which are only eaten cooked.....
Hi guys, my main line when it comes to eating food plants irrigated with grey water is this: "do you read the ingredients list of all of your cosmetics, shampoos, soaps, detergents etc. that enter your grey water system? If you do, and if you're happy to eat them via your veggies, great. If not, don't." Most people don't do that background reading though, and for those that don't - the list is probably fairly long and forbidding.
Sometimes in a dry period in the summer, when we have a bath - we'll avoid soaps and shampoos and syphon the water out to the polytunnel. If there's soaps/shampoos in the water, we don't bother - even though it's health store stuff.
However one way to recoup the nutrients is to route the grey water to a comfrey bed. Harvest the comfrey and use it as a mulch on your compost heap or direct on veggie beds. Really noxious stuff may still be transferred, depending on plant uptake rates. But if you're relatively careful with what you buy, this method is good for "obtaining a yield".
Hi Steven, Yes it is safer to use separated grey water than raw sewage, that's a good start… but bear in mind that if you are feeding food plants, you need to be happy with the ingredients going into your irrigation mix. What are the ingredients in your shampoo, soap, washing detergents, cosmetics etc.? Make sure that you are happy to put these on your vegetables.
Fruit and nut trees similarly.
If you are in an arid climate, then it may be well worth using the irrigation water. If you're not, then have a longer think about it. What is the practical advantage of using the grey water for irrigation? If it's simply to say that you're reusing it, then that isn't necessarily reason enough.
One option to lengthen the chain of connection between source and food plants is to plant comfrey… but I'm repeating my last post here.
Summary: it's safe if the ingredients going into your grey water are safe. Paradoxically, urine would be cleaner from a toxicological perspective, and much higher in nutrients.
Thank you for your reply. I have thought a lot about what actually flows through our drains and into the greywater tanks. Too many chemcals...What I have actually done is set up three tanks for greywater to filter through. I dug a trench big enough to connect two "pigs" to the system. By the time the overflow water gets out to the third tank would it be more usable?
From reading your posts, if I plant Comfrey between the greywater tanks and the garden space, would that clean up the drain water enough to be useable for edible plants?
It depends completely on what you send down the drain. I have some Permie friends and I'd say that they could grow watercress in their greywater pond as it leaves the house (at a pinch…) and other clients for whom recycling their grey water to edibles just wouldn't be a good idea without extensive filtration in a constructed wetland system first.
Art Ludwig's website is fantastic though and may well provide you with a clearer second opinion. I'd say if you still want reassurance or clarification try it at http://oasisdesign.net/
The system you have sounds really good - and I'd guess that you're careful with what you buy in terms of cleaners of self and surfaces - but if you're not happy with all your "irrigation ingredients" then route it to a biomass crop rather than a food crop.