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Does using greywater on your fruit and vegetable garden affect your health in a negative way?

Greywater is the run-off or cast off water that lolls about when you do normal washing around the home. The sink water when you're doing the dishes, the ejected liquid that comes from the laundry, etc. Most of it involves the suds and afterwash of soapy conditions.

Will eating the fruits of plants fed greywater do anything to a human that normal watering from the heavens above (rain) or from the tap (without rinsing through soap beforehand) won't?

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I think kitchen sink waste is not considered good greywater for anything - given the food/fat/meat/etc in the waste water. –  Tim Jun 9 '11 at 3:21
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4 Answers 4

It is not recommended to use greywater on vegetables that you will eat directly. E.g. salads or roots. They say greywater from bathing and laundry can contain bacteria like E. coli that can get on the food and make you sick.

Greywater designs that I've seen in books and on the web typically send the water through some kind of natural filtration system (e.g. a pond / marsh) that cleans up the water before you send it to the rest of your landscape.

It sounds like you don't have this. I'd play it safe and use the greywater for ornamental plants -- and then as Doug T. mentions in his answer, test it on something you aren't in love with first.

There is a wide variety in recommendations for greywater use -- including a failure to standardize on the definition of greywater. (Some classify dish washing water as greywater, others classify it as blackwater.) See, for example, these sheets from U Mass and New Mexico State U.

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Adding soap to water allows the water to dissolve oils. However pure water, as we all know, doesn't mix with oils. Since plants contain many vital oils and lipids crucial to their life, and rely on how these oils interact with plain water they absorb, soapy water would alter the fundamental chemistry at work and could only be toxic the plant.

So it really depends how gray your gray water is. Pure water is always best, but you might be able to get away with some very unsoapy gray water. I recommended testing on a plant you don't really care for.

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If grey water detergents were such a problem for lipids and vegetable cells, then the much more concentrated household detergents (ie. soap and dish-washing liquids) would be a serious health problem. Also, as Cape Water Solutions notes, household detergents are actually known as fertilizers due to their phosphate content. In fact this is their main problem in waste water - detergent-phosphates can cause algal blooms in water courses and lakes. –  winwaed Jun 20 '11 at 19:10
Also, mild soap sprays are sometimes recommended for insect control. –  bstpierre Jul 1 '11 at 1:21
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Greywater is safe to use on fruit and vegetables as long as the fruit and vet are rinsed before they consumption. Exactly as you do with store bought goods.

The definition of greywater is not universal. Typically greywater is defined as water from baths, showers, hand basins, and laundry machines, however, on occasion dish-washing water is incorrectly grouped as greywater too.

The soapy content of greywater is known to serve as a fertilizer to any plants that are watered with it. It is typically advised that a phosphate free laundry detergent be used as laundry detergents can be high in Phosphates. Cleaning detergents that contain bleaches or other strong chemicals should also be avoided.

Greywater does contain bacteria but so to does cow's milk, (Many of us still drink milk) and let us not even start the mention the millions of bacteria that are found in healthy soil/dirt. Bacteria in greywater is very light sensitive and what this means is that when greywater is exposed to sunlight the bacteria die off, leaving behind nutrition for the plant.

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I always wash my vegetables before I prepare them. However, many years ago a neighbor gave me tomates watered with washing machine water. I washed it and ate it and got sick as a dog! Seriously, just thinking about it makes me gag still after many years. My very good neighbors just gave me beautiful yellow onions..but they have been watered with grey water. I don't even know if I made onion soup that would help me. Intellectually I know they would me fine, but the old memory is still there. Just be very careful!

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