[Greenbuilding] reducing salts in domestic greywater (for use in the garden)

[YankeePerm at aol.com]

Ruben:
     Since there was no other reply, I'll give a stab at this.
     The importance of the salt load of your greywater and urine depend upon 
three factors:
1)   Your climate, especially rainfall. Obviously some leaching will avoid 
problems High evaporation potential means more water is lost at the surface, 
allowing salts to concentrate there.
2)   Your soil.   A nice loam will hold lots of nutrients whereas you get 
leaching to ground water more readily with a sandy soil, adding salts to ground 
water, or if you have heavy soil, percolation is slow and salts are more 
subject to build up.
3) The plants to be irrigated.   Banana or tomato tolerate very little salt, 
though I've irrigated tomatoes with greywater and urine (mixed) in Florida 
with good results.   One need be judicious. Some plants are very salt tolerant.   
The best way to fertilize an inland coconut palm is with table salt (NaCl).   
There are relatively salt tolerant VARIETIES of tomato, to go back to the 
earlier example.

Young seedlings (as opposed to trees that are grown from seed instead of 
grafted, also known as seedlings) are very salt-intolerant, though I supposed that 
there is wide variation there, also.   As a general rule, irrigate freshly 
germinated plants only with fresh water.

The Ludwig system allows you to target certain trees that you presumably 
selected for salt tolerance. 

I've gardened in Kansas with 20" of rainfall, Georgia with 30+, Massachusetts 
with seasonally ideal rain for crops, and now in Florida more than 4' of rain 
annually (but that is an average of wildly fluctuating annual figures.)   
I've never had problems with salt buildup in my gardens where I've routinely used 
grey water and urine.   One needs to be conscious of plants that are 
susceptible, which tend not to need extra fertilizer.   Banana, which is salt 
sensitive, is sometimes grown in grey water swales.   

You have fewer choices of plant species and varieties in low-rainfall 
climates because soils tend to have higher salt loads already.   Heavy soils should 
be a problem in theory, but in heavy clay in Kansas and Georgia, I had no 
problems.   Of course the amount of grey water and urine that a family produces is 
pretty widely dispersed if used to grow much of the family's food.   

Mulching, almost always a good idea, really helps limit the buildup of salts 
near the surface when irrigating with greywater and urine.   Partly, this is 
due to the restriction of surface evaporation.

Plants stressed by soil salts show tip 'burn' of the leaves and may start to 
die back from the top (especially true of woody plants.)

I hope that I've been helpful.   I could have answered more specifically if 
you said where you live and described the environmental factors.

Dan Hemenway

In a message dated 5/2/08 1:35:15 PM, 9watts at gmail.com writes:


> I'm still trying to come up with a simple system for using my greywater 
> (and I hope urine from a urine-diverting toilet) to augment my garden watering 
> (using rainwater) in the summer months. I have read Art Ludwig's "Create an 
> Oasis with Greywater."
> 
> My question is whether and if so how it might be possible to reduce the 
> salts that both greywater and urine contain? The daily flows from our household 
> of these two combined (which does not include laundry water) are something 
> less than 10 gallons per day in the summer.
> - dilution with (more) rainwater?
> - change soaps/reduce their use?
> - install a grease trap under kitchen sink?
> - ...
> 
> Thanks everyone.
> 
> Reuben Deumling
> 
> 





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