Fruit trees and vegetable plants grow well with graywater. The risk is that graywater may contain bacteria, and if you eat fruit and vegetables covered in graywater (and therefore bacteria), you may become sick.
If the fruit or vegetable is going to be cooked, any bacteria present will die during the cooking process. This removes the risk.
A substantial crop of tomatoes, irrigated with graywater. Care is required to ensure graywater does not come into contact with the fruit.
An interesting study concluded that tomatoes are not affected by graywater irrigation.
Greywater and vegetables / low fruit
Where the edible part of the fruit or vegetable is above ground, and it is eaten raw, the graywater must NOT come into contact with the edible parts.
This can be done by bucket (very carefully) but is labor intensive. High flow rate dripperlines (such as Irrigray) apply the graywater directly to the soil zone, and seep into the soil immediately.
So long as a layer of mulch covers the dripperline and soil, there is virtually no chance for the edible component to come into contact with the graywater.
Where the edible part of the vegetable is below ground (e.g. potato, carrot, onion), graywater will come into contact with the vegetable.
If the vegetable is cooked before eating, the risk is removed by the cooking process.
If the vegetable is eaten raw, the risk can be reduced by washing the vegetable, peeling, then washing again.
We do not recommend growing the following types of vegetables, if they are to be eaten raw:
Because the skin is rough, radish is difficult to clean. Commonly served unpeeled, there is a risk of bacteria remaining on the surface.
Salad onion (including scallions etc).
Due to the onion’s layered structure, there is a chance (albeit small) of bacteria being caught within the onion, presenting a risk if eaten raw.
Lettuce is an excellent example of why the first reaction of authorities is to prohibit irrigation of vegetables with greywater.
If the lettuce is irrigated by sub-surface dripperline (under a mulch cover), the lettuce leaves will not come into contact with the greywater.
However if the lettuce was irrigated with greywater by a watering can, bacteria would collect on the leaves, and present a health hazard as lettuce is rarely cooked, and the cleaning process is unlikely to remove the bacteria.
What about soap in the fruits and vegetables?
We are yet to find an appropriate scientific study that has measured how much soap is actually contained inside the fruit or vegetable.
The consensus view is that only tiny amounts could be present and only at a molecular level.
Keep in mind how much the soap / shampoo / conditioner has been diluted by the time it gets to the plant.
Consider how much your body is ingesting through other daily activities (brushing your teeth; direct skin absorption of soap, shampoo and conditioners; soap residue on plates that you eat off etc.)
Another consideration is how much pesticide do your store-bought fruit and vegetables contain?
Yuck! Eating vegetables with water I have showered in or washed my clothes in!
This is a common response – and quite natural. Think about what your vegetables are growing in now; decaying compost, worm castings (and droppings), fertilizer, bird droppings, all manner of less pleasant ingredients than body oils and dried skin.
Graywater irrigation of fruit and vegetables is of course personal choice. No one is forcing you to grow your fruit and vegetables with graywater. However, on balance it would appear home grown foodstuffs will have less contaminants than commercially grown produce.
My local regulations prohibit or advise against the use of graywater for vegetables.
Contact your local health department and find out why. Many regulations / recommendations are written to cope with the most common practices, such as people considering bucketing water onto their lettuce and strawberries etc. This type of irrigation with graywater is risky, because of the potential for bacterial contamination.
Graywater dripperline technology has evolved enormously over the last 6 years in countries such as Australia. The new dripperline technology has only recently arrived in the US, and health department regulations or recommendations take many years to catch up.
We are not recommending that you break the law. We are simply suggesting thinking about why the law was written in the first place.
This chapter is written as general advice, based on our own research and experience. We recommend conducting your own research and / or consult local authorities before deciding what’s best for you.