this post was submitted on 12 Dec 2025
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Hydroponics
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Comrade, it is not distilled water and neither is your RO.
Distilling separates fractions in the liquid by boiling point. That's why it's not just boiling a pot of water and catching all the steam. You need to have some sort of idea of what you are separating and ensure you are collecting the distillate at the correct temperature (based on the atmospheric pressure). RO is - in an extremely simplified description - a filter, where particles that are small/soluble enough will pass through the membrane if sufficient pressure is applied.
Distilled water will have zero conductivity, RO will have some.
As an aside because I am insufferable: your meter says TDS but it's measuring conductivity. They are often used interchangeably because TDS is a massive pain to test at home. If you are always measuring the same thing, it's fine to use conductivity as a surrogate, but you can't compare the conductivity of sugar water to salt water and assume you have a good idea of the TDS.
I won't venture to comment about its use on plants but to folks asking about drinking it in the comments, please don't. Even if it was distilled it's hanging out in an environment full of airborne life and wouldn't remain sterile for long.
(Credentials? I got a D in mass transfer 20 years ago but I still somehow manage to work as an engineer and do a lot of lab work too. But nothing I've said isn't readily verifiable)
True, but it also includes the step with the condensation collumn and collection of the condensate. Boiling isn't linear, it can also turn into vapor at room temperature, especially with air movement.
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.
Dude, stop saying that. That's rude to yourself! ๐ค
You're just telling me concerns you have, not more. That's great. I like discussions and discourse, this is why we're here! And this is how people get smarter.
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.
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.
I personally just treat it just as rainwater. Never ever would I drink something of it, and in case of rainwater, there's some visible debris floating around. In the condensate maybe too, we'll see!
(Credentials: chemistry profession)
I'd be concerned about lint or micro plastic nylon (etc.) fibers in there. I doubt the lint filter is collecting 100% of the fibers before the warm moist air gets blown over the evaporator/condenser coils where condensate is collected.
Yep, seems like it. I just looked at it closer in a glass beaker and saw lots of floaters around.
I still think most of it is cotton fibres, and even if it's microplastic, it is mostly inert and plants don't care much about it. I flush out my substrate every few months anyway, and not use it for food contact plants.
Fair - most of my distillation experience is not on water so I goofed in this fact (oversimplified)
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.
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
How do I use this information to make fireworks or booze?
Cs get degrees!
(I got 4 Ds in my academic career and I was grateful for each one lol ๐ฅฒ)