Author Topic: TDS levels and gray water watering  (Read 226 times)

jbclem

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TDS levels and gray water watering
« on: September 21, 2022, 05:59:26 AM »
With the drought restrictions here in S.Calif, I've been watering my citrus with gray water.  I've also started checking the TDS (total dissolved solids/salts) levels to make sure the gray water isn't harming the trees.  But I don't have any reference levels as to what levels are too high.  I have some old citrus trees in the ground and also some young ones.  The soil at my house is silty sand/sandy silt and drains well.

My tap water is showing about 310 on the TDS meter.  Since I've started using soap nuts instead of laundry detergent,  the laundry gray water levels have been 300-350.  With regular detergent I get 400-500, and the highest I've measured so far was 650 from a 5 gal bucket of Oxiclean and water.

I'm also watering a loquat and a pear tree with the gray water.

I've read that citrus is sensitive to salt but haven't found any TDS reference levels.  Does anyone know what I should be watching out  for?

John


Oolie

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Re: TDS levels and gray water watering
« Reply #1 on: September 21, 2022, 12:57:54 PM »
I might hesitate to put the oxyclean down the drain until it has been deactivated. The bleaching effect will kill any microbiota, and could potentially damage roots.

Think of it as bleach without the chlorine.

Vegan Potato Man

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Re: TDS levels and gray water watering
« Reply #2 on: September 21, 2022, 09:30:31 PM »
TDS is derived from EC (electrical conductivity)

Tds/ec measurement does not tell you what is dissolved, just how much electrically charged particles are in solution. Without testing a sample there's really no way to be sure what is in it.

That said, assuming you haven't been pouring salt down your drain, I would assume it would be safe since the numbers you mentioned aren't very high to begin with.

If you want to be sure, I'd suggest getting a test done.

Oolie

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Re: TDS levels and gray water watering
« Reply #3 on: September 21, 2022, 10:42:02 PM »
Good point, a key problem with high salts is going to be chloride buildup, but you will usually only see it if the soil gets dry enough and there is enough chloride present. If you see burnt leaf edges, that's usually the first sign that your root tips are not happy.

pagnr

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Re: TDS levels and gray water watering
« Reply #4 on: September 22, 2022, 03:54:22 AM »
TDS is derived from EC (electrical conductivity)
Tds/ec measurement does not tell you what is dissolved, just how much electrically charged particles are in solution. Without testing a sample there's really no way to be sure what is in it.

As I understand it you still have to watch the EC of water you apply, including liquid fertiliser mixes ( and ultimately dry fertiliser that dissolves in water ).
Basically if NaCl salt has an EC, then so does CaCl, MgCl, and also MgSO4 etc etc. all common component of fertilisers.
Yes some are going to be beneficial nutrients and some more harmful, but a very high EC from any compound can be a problem, particularly in pot plants.

Vegan Potato Man

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Re: TDS levels and gray water watering
« Reply #5 on: September 22, 2022, 12:41:55 PM »
TDS is derived from EC (electrical conductivity)
Tds/ec measurement does not tell you what is dissolved, just how much electrically charged particles are in solution. Without testing a sample there's really no way to be sure what is in it.

As I understand it you still have to watch the EC of water you apply, including liquid fertiliser mixes ( and ultimately dry fertiliser that dissolves in water ).
Basically if NaCl salt has an EC, then so does CaCl, MgCl, and also MgSO4 etc etc. all common component of fertilisers.
Yes some are going to be beneficial nutrients and some more harmful, but a very high EC from any compound can be a problem, particularly in pot plants.

650 is not a very high TDS measurement for established plants, but you're correct that we don't have a sense for what compounds are dissolved. Judging by the small difference in measurement between the tap water and soap nut water I would guess that would be ok at least. OP could look at their municipal water quality report to get an idea whats in the ~300 ppm of their tap water.

Aside from getting a sample tested for water quality, OP could dilute the grey water further, but that would probably be negligible (talking about the soap nut water) since the difference in tds isn't all that much.

I would be concerned about the other laundry detergent though.

Quote
As I understand it you still have to watch the EC of water you apply, including liquid fertiliser mixes ( and ultimately dry fertiliser that dissolves in water ).

This is correct, assuming you know the quality of your source water. When it comes to hydroponics its usually recommended to start with RO water as a source to start clean. When you start with a high ec source water, especially if you don't know its specific components, you run the risk of nutrient toxicities, especially when it comes to micros and (to a lesser extent but more in this case) sodium.
« Last Edit: September 22, 2022, 01:29:13 PM by Vegan Potato Man »

pagnr

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Re: TDS levels and gray water watering
« Reply #6 on: September 22, 2022, 05:28:55 PM »
My tap water is showing about 310 on the TDS meter.  Since I've started using soap nuts instead of laundry detergent,  the laundry gray water levels have been 300-350.

Yes that is not a big jump. Soil should act as a buffer, and soil organisms should consume some nutrients too from soaps and detergents.
That could depend on soil type, very light soils might offer less buffer and microbe activity,
As you are in a drought regime, you may not be able to apply any non grey water as usual, or rely heavily on grey for multiple irrigations ?
Check the ingredients of the Oxiclean, there may be a sodium component as a stabiliser ?

 

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