Should be fine. The more simple, basic soap you use, the better, as it will get broken down by the soil denizens more easily. There are two main concerns with soap: anything anti-bacterial, or soap with phosphates (formerly in laundry detergent, but has been massively reduced in last 20-30 years, but that's more about not getting them in the water). You can generalize this to those soaps with more complicated chemical additives (pretty obvious).

Of course, simple common sense guidelines apply, like don't pour over leafy plants you intend to eat, more caution around food plants, etc. That's more about just not getting soap coating the things you eat (can probably be washed off anyway). Perfectly fine on compost pile, too.

Agree with all of that.

Some of the synthetic detergents are a bit slower to biodegrade, but I doubt this would be a problem unless you're putting all of your wastewater on a small area. In that case you'd probably want to use 'biodegradable' products.

Phosphorus is a major plant nutrient so the ground or the compost is the best place for it!

I found this link somewhere on my computer, for what it's worth.

https://vric.ucdavis.edu/pdf/fertilization_Householdwastewater.pdf

I wouldn't use it on food crops or in compost that goes for food crops. You don't know what's in soap products today and you don't know if they break down into edible chemicals. With all the chemistry today making us sick, why would you want to take a chance with your body?

Valid point about not using on food crops, but for compost? We don't eat compost or dirt, either. This subject is really for someone with a background in environmental chemistry (anyone like that here?), but basic soaps get broken down biologically. For the most part, we do know what they break down into - and they don't need to all break down into edible chemicals, just things that plants can grow in.

^^ What armoured said.

I'm somewhat knowledgeable (as an env. chemist :-) on this topic but I don't have anything in black and white.

Actually we DO know what is in these products, because it's on the label. Consider that you're using this stuff on your dishes, clothes, and the outside of your body. That's a much more direct exposure than putting it in the compost or on the ground where plants grow.

Not saying all detergent ingredients have zero toxicity, because they don't - if they were non-toxic there wouldn't be a Tide Pods crisis. :-P But it's important to keep things in perspective - it's all about the dose. Me, I would use soapy water on the lawn or around trees and shrubs and only sparingly around vegetables, if I was doing it daily. This Old House hooked up a graywater pipe for a house in California once, to drain the washing machine out to the landscape with multiple outlets. They told the owner to switch to biodegradable detergent. Good advice.

Some of the synthetic detergents like phenol ethoxylates are suspected of being endocrine disruptors for aquatic life, but at levels much higher than observed in wastewater effluent or rivers. They are a little less degradable in the sewage plant than old fashioned soaps. What that means for the garden is hard to estimate - too many variables.

Laundry and dishwasher water I would be the most concerned with simply because of the amount of detergent used. Washing hands or dishes doesn't use that much. But, again, it's all in the amount per area per time period, so use your judgement.

armoured, that's a great article you linked. I had not considered borax or other borates - boron can be toxic to plants in high amounts and does not break down or go away (it's an element). That's one of the things they probably leave out of the 'biodegradable' products that are more suitable for daily discharge into your yard. If it's an occasional dishpan full I wouldn't worry about it, but if you're going whole-hog with graywater recycling, you should research it and look at the products you're using.

it does not 'all' go into the roots, nor into the parts that we eat, and even then, likely not in quantities that are meaningful. Again, most of these soaps and detergents are already used in ways that mean close contact with skin, food, etc - likely in concentrations more meaningful than after a process of composting (decomposition), soil filtration/loss, dilution by many means, and uptake by plants. (I and others have already cautioned against direct application on edible parts of the plant)

But in the end, if you're not comfortable with it, there's an easy solution - don't do it. To each their own.

Thank you for the responses everyone. I really love learning from this forum and hope one day I may be able to contribute to it when I've learned enough about gardening to be confident in offering advice.

When some of you mention basic soaps that would be easiest to compost, do you mean soaps like dr brommers? What other good cheap brands do you recommend?

I'm assuming that the shorter the ingredient list the better here?

I don't have any specific soaps to recommend, but yes, ones listed as biodegradable or with the shortest list of ingredients possible. Probably easiest to search for specific brand names. Some no-name or house brands at grocery stores might also be the same as better-known brand names. Avoid any with terms like anti-bacterial.

Agreed on the anti-bacterial. Ingredients in general are a like reading a chemistry set, even if they are biodegradable (if I gave you the full chemical name of old fashioned lye soap made of beef tallow and lye, it would hurt your brain). Probably best to look for keywords like biodegradable, eco-friendly, and septic tank safe. Sorry if some of those sound like cliches but that's really the most direct way.

Here's an article listing brand lines of biodegradable products.

https://www.thegoodtrade.com/features/natural-eco-friendly-cleaning-products-for-the-conscious-home

7th Generation is one that I've used before (mostly their recycled paper products) so I looked at their lineup, picked a random dish soap and looked at the ingredients. Most are plant-based, which means they are not made from petroleum (the other industrial chemistry set besides plants). This doesn't necessarily mean a chemical is bio-degradable or even non-toxic, but if their product says biodegradable, then it most likely is to a great enough extent to be OK for the garden. Just my opinion.

As for the safety of degradation products (as mentioned earlier in the thread): when the vast majority of these things break down, they turn into pretty simple and nontoxic molecules. It's rare to see something biodegrade into more toxic stuff. Not unheard of, but it usually happens with things that are toxic to begin with - DDT, chlorinated solvents, etc. Detergents are usually toxic only when there's too much of the original compounds in waterways.

I've had 20 years experience running greywater straight out to trees, in a cold desert climate. The willow and poplar trees loved it and got bigger much faster than all our other trees. Wild mint and stuff grew like crazy on it.