Expected ppm of RO water?

[nhman]

So.......after having some, er "issues" with my collection, I got smart and bought a water ppm meter (It adjusts for temperature too! I'd highly recommend this tool for all that use water!)
I found that my home water system wasn't working all that well. (HARD well water runs thru a water softener and then an RO unit.) My orchid watering water was about 75 ppm and I was having root loss and leave death.
So I replaced the water softener and RO unit. I am getting RO at about 40 ppm or so now.
While going about this process, I began "recycling" water from two dehumidifiers in my house (ppm of 0.5 to 10) and from the air conditioner in the orchid growing room. My average ppm in the orchid watering tank went down to under 20 ppm. The plants perked up and looked MUCH better.
The question that I need to know is this - is this normal, high or low? Better yet, is this level of ppm "safe" in watering my orchids????
Advice and thoughts appreciated as always.

[Gin]

What kind of water softener are u using ? hope not the type that uses salt , my ro runs about 6 it is straight county well water going into it . I add some straight tap to it for the minerals , I think 20 should be fine ..

[RosieC]

As Gin has said, water softeners that use a salt are actually bad for orchids.

They work by replacing the calcium with something else (can't remember what now) and the thing they replace it with is even worse for you plants than the calcium.

RO water is used by a lot of folks on Orchid Board though, so if it is just an RO unit you should be fine.

[Ray]

Originally Posted by RosieC

As Gin has said, water softeners that use a salt are actually bad for orchids.

They work by replacing the calcium with something else (can't remember what now) and the thing they replace it with is even worse for you plants than the calcium.

Most water softeners replace the calcium-, magnesium-, and iron carbonates with sodium, and it is the excess NaCl that can be bad for plants. BUT... softened water is actually easier for an RO unit to clean than in the carbonate-laden tap water.

I think something is wrong with your RO unit (or meter), as you should not be seeing beyond the single digits on dissolved solids.

[Masdyman]

As Ray has stated the RO TDS reading does seem high for RO ,but not for orchids 40 ppm is probably less than rain water so is ok .But feel for a RO unit the reading should be lower .
I personally wouldn't use any waste water from softeners,dehumidifiers etc .

[Ray]

Why wouldn't you use water from a dehumidifier? After all, it is just distilled water - the difference being that you're putting the energy into condensing what is already in the air, rather then doing so after putting energy into vaporizing it.

[Jerry Delaney]

Originally Posted by Ray

Why wouldn't you use water from a dehumidifier? After all, it is just distilled water - the difference being that you're putting the energy into condensing what is already in the air, rather then doing so after putting energy into vaporizing it.

I don't know, Ray. I have heard "tales" when I was whole selling tropical fish not to use water from ac or dehumidifiers. Some species succumbed to high copper levels (supposedly). I have no real proof that this was the real problem and even if it was, would it make a difference on plants. I do know from experience that ONE copper fitting in a 316ss line is enough to render any mammalian cell culture media toxic.
As to EC, TDS or what ever you may call it, I agree that a reading of 40 would seem to indicate some sort of problem. I would make sure that your filter housing has no nicks or gouges in it that may allow some leakage around the o-ring. Also, if your cartridges are old, it doesn't take much more than a pin prick to cause a problem. By the way, Ray is correct in that softening the water first greatly improves RO filtration and extends filter life.

[RosieC]

Interesting point on the softened water Ray. So if you soften before going through an RO unit it's fine (and even easier on the RO unit). Interesting to know.

[Ray]

Yeah, apparently the sodium chloride flushes from the membrane easier than do the other minerals. I have no first-hand experience with that, as I don't have a softener, but if anything, all it will do is potentially lengthen the period between membrane replacements; it has no effect on the purity of the output stream, as that is strictly speak a size thing.

I ran across a really interesting graphic from an old water quality organization, showing the relative size of stuff relative to RO treatment. Modern TFC membranes are good down to about 0.0007µ.

[Royal]

Originally Posted by nhman

So.......after having some, er "issues" with my collection, I got smart and bought a water ppm meter (It adjusts for temperature too! I'd highly recommend this tool for all that use water!)
I found that my home water system wasn't working all that well. (HARD well water runs thru a water softener and then an RO unit.) My orchid watering water was about 75 ppm and I was having root loss and leave death.
So I replaced the water softener and RO unit. I am getting RO at about 40 ppm or so now.
While going about this process, I began "recycling" water from two dehumidifiers in my house (ppm of 0.5 to 10) and from the air conditioner in the orchid growing room. My average ppm in the orchid watering tank went down to under 20 ppm. The plants perked up and looked MUCH better.
The question that I need to know is this - is this normal, high or low? Better yet, is this level of ppm "safe" in watering my orchids????
Advice and thoughts appreciated as always.

Just a clarification: ppm (parts per million) is a unit of concentration, not something in the water. Your meter probably measures TDS (total dissolved solids) and expresses the reading in ppm. 1 ppm = 1 mg/l

Installing a softener upstream of an RO unit would just be adding more "stuff" for the RO membrane to remove.