I have never heard it advocated by any of the dozens (possibly hundreds) of articles i have read on aquaponics and permaculture so why not?

I envision greywater flowing into a grow out tank and then overflowing out into a traditional irrigation system.

Here is my attempt at a picture:

If water is so valuable that you are willing to forgo on the soap then sure. The nutrient obtained would be almost negligible and not worth the effort I suspect.

Thanks for your reply

Amedean Messan wrote:If water is so valuable that you are willing to forgo on the soap then sure. The nutrient obtained would be almost negligible and not worth the effort I suspect.

I plan to make my own soap. Just lye from wood ash and some lard. I am under the (possibly false) impression that this wont hurt the fish and it will repel certain pests in the garden. I will be in SoCal where it is hot year round, and according to worldweather.com, in the wettest month (feb) receives only 3.13 inches rainfall average and the driest (july) .07. That would make the water very valuable indeed because irrigating the garden any other way would be too expensive.

From what i understand, water from fish tanks has levels of nutrients that are well above "negligible". What leads you to suspect that they would be in this case?

I imagine this doing everything that a regular, closed look system aquaponics setup would do just without any electricity. The water splashing into the sinks and bathtubs and then being poured into the grow tank would aereate it and then the constant inflow of new water would prevent nitrates from becoming too concentrated (in theory). The nutrient rich water (up for debate) then goes into the garden and both irrigate and fertilizes. All of this occurs without any extra electricity from the pump. This would also eliminate a lot of the up-front labor to set up a system since the only thing one would have to do is to build/ obtain a grow out tank, put it under the grey water output and install an elbow pipe for overflow that is directed into the garden.

That being said, none of that matters if simple soap is harmful to fish.

Some considerations:

1. What comes out of the shower. No soap for sure, but you also have urine (people pee in the shower) and a small amount fecal matter. That means you may be feeding your fish (do you plan to eat the fish?) with pathogen-rich water. Not good.

2. The water coming off the fish tank is nutrient rich, but you have to have some way of aerating the fish tank. No oxygen in the water, fish die, you sad. Are you planning to take showers all day so you can oxygenate that water on a constant basis? If you see indoor fish tanks with large fish, they are oxygenating at an extreme rate compared to this design. This might work with minnows, but then you lower the quality of the water, as minnows don't do much nutrient cycling.

3. I don't think that fish would like your wood-ash and lard lye. The thing with fish tanks is the pH needs to be to their liking, which means constant measuring.

4. Not only the fish will be getting the pathogens, but the plants will be too. Unless you have a system in place to kill the pathogens.

If you have an excess of grey water, just put it into a tube and throw it on ornamentals in the spring/summer/fall; in the winter re-attach to sewer because you will be (assuming cool/cold temperate) inundating already wet ground with pathogenetic water.

Grey water can be successfully managed in reed systems with small fish who don't need a lot of oxygen. But this is not your case.

William

The other problem to deal with is temperature shock. Putting hot shower water into a small tank will change the temperature quite rapidly, another thing most fish don't like.

If you put the aquaponics part after a holding/settling tank or initial reed bed, it will stabilize the temp and pH.

Yeah. Add one more "earth tank" with reeds and a tube coming out of it and most of your problems are solved. Biofilter yuckies.
William

The comment about winter still holds. Biofilters don't biofilter in the snow.
And aeration of the tank of fish, unless you want a tank full of dead fish.

You might find threads here about aeration rates on tanks in aquaponic systems.

W

Hey Dan,

Not sure where you're living, but if you have a nice warm year-round climate you could do this. However you'd need several layers of filtering before you got to the fish. You could run the water through a rain garden / water filtration pond, then through another one, and possibly a third before letting the fish have the water. Some plants that you can eat grow well in these ponds, such as cranberries.

If your air temperature ever gets cold this would not work in winter. You'd have to keep your fish alive and healthy some other way in winter. You'd also have to figure a way to do nitrification during a drought.

There are some guys out in Phoenix, AZ. that do exactly what you are describing.
Check them out. http://gardenpool.org/