PPM's Reverse Osmosis, Distilled or Tap?

Up front, I am a novice on DWC!

Now that is out of the way I have a statement, then a question.

It is my understanding that PPM are used in DWC as a gauge to determine the content of particles in the water. When starting out using reverse osmosis or distilled water, your have a very minimal particles in it or “very close to it”, at this point, we have a good base of low PPM that we can compare against. This allows us to determine how many nukes or particles that reside in the water, supplying a way to monitor intake of food or water the plant is partaking of…


During seedling stage to early veg stages of the plant, which are during the stage of growth that “some” would go light on the nukes Now if you are using RO water or distilled, and you are going light on the nukes already, then the water should have a low PPM to start with.

So my Question is,

During times of low PPM, during the first few weeks of growth, How would it effect the plant if we just used normal Tap water that is full of PPM’s, “example, my house is about 570ppm from tap”

but my thinking is, if you are not in the state of growth that you max out the PPM, are we not able to use just tap water with “high PPMs”, with the exception of the PH being adjusted properly?

Are there particles that the plant JUST does not like?

Or is there some other factor I am missing?

Does anyone have a take on this? I do apologize if this does not make sense to anyone.



The high PPM/TDS are usually calcium, lime, and some iron. These values though represented in the meter, do not have any viable nutrients available to the plant.

Three basics need are required for a plant to grow.
Let’s discuss the N-P-K ratio.
The NPK ratio contain the 3 basic elements of what a plant requires for growth. To be clear, there are other elements in play as well, such as copper, iron, sulfer, calcium, magnesium, and so on, but for simplicity let’s keep it to three.

There are extremely small amounts of NPK in your water, but we are talking micrograms if any. This is not enough your tap water to allow growth in your plant. So we as growers have to add this to the water.
NPK ratio is Nitrogen-Phosphorus-Potassium. (Periodic table of elements the abbreviation is K)

So when you’re growing hydroponically we have to ADD NPK to the water in addition to the current PPM/TDS number that is existing. Even as a seedling or young plant, when growing in hydro you’ll need to add approximately 200PPM of NPK for it to actually grow, because there are no nutrients in the water.

I hope this clears things up.


Got it, it does help!

I pulled out of it, what I was needing for sure.

I understand why it is done, but wasn’t for sure if, during that first couple of weeks it was as important.

I see why it would be the same throughout all stages of growth now.

Thanks for the time you took to input the info.!


My answer ought to really cloud the waters. This is how I seedling:

  1. I use municipal tap water… PPMs are between 60-120 (depending on water temp) or dehumidifier condensate (ppm 12-25) for all water applications
  2. I germinate in a glass of tap water with a few drops of H2O2
  3. I use Rapid Rooters for germinated seeds. I soak them in the following for 24 hours before I put seeds in them:

Tap water with the following nutrients per gallon:
1.25ml FloraMicro
1.25ml FloraGrow
1.25ml FloraBloom
1.25ml Calimagic
1.25ml Armor Si

For me that usually comes out to a total PPM of between 200-300. If it comes out higher than that, then I just add more tap water to the bucket until it’s around 250. This is where I also start managing PH, so I PH this solution to 5.8 as well.

  1. Once I get to the main system I use tap water or condensate the entire time.

As for the PPM make up of your water… that can only be determined by analysis. If you are using municipal water you can get a water report from your municipality - usually they are available online at no cost. You could have 250ppm water that doesn’t have any K or P in it, but has a ton of copper in it, by way of example. @Covertgrower has you squared away as usual.



Perfect, didn’t cloud any waters at all. and right on the track of what I was looking for!

Clear one statement up for me…

If after adding nutrients the PPM’s are too high for a smaller plant, he will add water to bring the PPM’s back down. Dilution of the nutrients, so they’re not so strong and burn the plants. @kw_Bat


That’s exactly right. With the way I am growing now, with one big reservoir (40 gallons, so I am putting 30 gallons of water in it), I usually mix up all my nutes in 15 gallons of water, then just add water until I hit the PPMs I want and PH it.


Thanks for clearing it up!

if i m doing the reverse math correctly…
that is 1.1 EC from the tap, do not use this water even in ‘soil’.!!!
that is really ‘hard’ water and not good for plants.!

i wonder if one day hydro growers will stop converting their EC meter to ppm/tds.??? LOL


The can be particles that are to big and not bio available top the plant


Get rid of the chlorine and i bet your seedling does just fine with it… but no guarantees, you have to try to see, but if i was a betting man my money would be on you being ok


It depends on if it’s calcium carbonate or calcium bicarbonate, one of them is viable for plants


So, outside of the seedling stage, this is how you grow with tap water.

You pretend it is at zero ppms and you add nutrients like you normally would, it’s that easy :wink:

So if your at 500ppm tap water, and you are mixing up a solution that you would normally take to 1000 ppm with RO water, then add 1000ppm to your tap water and take it top 1500ppms.

The reason you do this is just like covert said, it’s possible the plant is using nothing.

Where you need to be careful is in late flower and approaching 1600ppms because if anything in your water is bio available then the plant could begin to burn.

So i add nutrients like nothing is in my tap but i never exceed 1600ppm.


I can’t remember which one


So ill try to sit a jug of it out for a day or so.
If I test EC before and after it sets out, will i be able to see the data change in the testing? In other words, when the chlorene isnt present anymore, should the data show it?

No, chlorine is not conductive like “salts” and will not show up on your ppm/ec meter

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From what I’ve read just letting the water sit out with an air stone for 24hrs gets rid of chlorine but i have never bought something to actually test that statement with.

Maybe others have


Sweet, thanks a million, this is exactly what i thought, but i wanted to hear it out of experiance.

Thanks a million for taking the time.


You bring up a good point @TDubWilly maybe we should tag someone in the lab and ask? Honestly I’m doing the same thing you did. I went with what others did.