Expected ppm of RO water? - Orchid Board

nhman · #1 08-25-2010, 09:03 PM

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 · #2 08-25-2010, 10:15 PM

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 · #3 08-26-2010, 07:01 AM

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 · #4 08-26-2010, 10:24 AM

Quote:

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 · #5 08-26-2010, 12:23 PM

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 · #6 08-26-2010, 04:09 PM

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.

RosieC · #7 08-27-2010, 07:31 AM

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 · #8 08-27-2010, 09:50 AM

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 · #9 08-27-2010, 02:34 PM

Quote:

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.

nhman · #10 08-27-2010, 06:43 PM

Thanks for all of the input everyone!
I DO have a salt utilizing water softener "up stream" from the RO unit as my water is quite high in iron and manganese as it comes out of my well. It's nice to hear that I may NOT be poisoning my plants with this setup.
I am having our "water guy" come out and place a pump on the RO unit to attempt to "maximize" the unit's performance (apparently, there is an "ideal" pressure that these units function best at.....")
I'll keep all updated to see what this change does.
Again....thanks all!