this post was submitted on 12 Dec 2025
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Hydroponics

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Everything regarding hydroponics is welcome here - from your houseplant in LECA to big scale commercial farming.

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PSA: The condensate from your dryer is distilled water (slrpnk.net)
submitted 5 days ago by Guenther_Amanita@slrpnk.net to c/hydroponics@slrpnk.net
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It's the first time I own a dryer. When I poured out the water it has collected (a few liters per run) I quickly tested the EC and pH and found out, that it is almost identical to the one made by my reverse osmosis filter!
No wonder, since the dryer is basically just a big distillation machine.

Thats super neat. It will save me a lot of work filtering tap water.

I will collect it from now on and use it for watering my plants.

Why does it matter?

Plants really don't like tap water. Even in a country like mine, where no chlorine/ fluoride/ whatever is added, the dissolved minerals cause trouble. They will build up over time and make nutrients unavailable, even if you adjust the pH.

The buildup and nutrient lockout will harm the plants a lot in the long term, and you will have way more trouble checking and correcting EC and pH.

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[–] Arcanepotato@crazypeople.online 2 points 5 days ago* (last edited 5 days ago)

Not exactly. Gases, particularly CO2, can dissolve in it, and form carbonic acid for example. That's why it doesn't have a pH of 7, but 5-6ish.

Fair - most of my distillation experience is not on water so I goofed in this fact (oversimplified)

AFAIK the TDS is the TDS700 to be precise, which is for measuring nitrogen or something. It's a really shitty and inaccurate unit, which is why the EC is the preferred measurement for many hydro growers, including me.

I think I'm missing some jargon.

TDS700? This is the method I am familiar with for TDS: https://edgeanalytical.com/wp-content/uploads/Waste_SM2540.pdf

Measuring nitrogen is a massive fucking pain with gross reagents but I suspect the nitrogen I work with is a lot different than nutrient mixes in hydro lol. Anything that needs a digestion step gets shipped to a Real lab.

I guess using conductivity for nitrogen is more about assuming the nutrient is "pure" but in different concentrations so you are just trying to see how dilute or concentrated it is based on the conductivity. I suppose that means it's it's a surrogate measurement not a direct measurement, which is why EC would be better than an actual TDS for that.

What you're saying is that the dissolved/ dispersed things aren't detectable by condictivity, did I understand that correctly?

If so, then there have to be visible particles. I will do further experiments and boil some off to see if there are residues forming.

Yes, but specifically that there are dissolved things that are not detectable by conductivity. No conductivity doesn't mean the solids must be non-dissolved. Not all things dissolve by breaking into ions. And not all ions give the same conductivity.

I misunderstood what you use the conductivity for - if it's to tell the strength of a known composition of unknown dilution, that's a pretty straight forward correlation.

Take for example the use of EC for TDS in drinking water, as described here: https://health.canada.ca/publications/healthy-living-vie-saine/water-dissolved-solids-matieres-dissoutes-eau/alt/water-dissolved-solids-matieres-dissoutes-eau-eng.pdf

The method most commonly used for the analysis of TDS in water supplies is the measurement of specific conductivity with a conductivity probe that detects the presence of ions in water. Conductivity measurements are converted to TDS values by a factor that varies with the type of water.(18,19)