My RO water still has 10ppm TDS - What is it?

Tom Wood

Guru Class Expert
Jan 24, 2005
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Kerrville/Austin, Texas
I'm still not getting a good response from the plants, even after going to 100% RO water.

My water starts as 510ppm, 24Gh, 16KH, that also goes through a whole-house salt-based water softener before being processed by the RO unit. The end result is 10ppm TDS. But I read here:

"Purity is determined by two things, first the "reject ratio of the membrane (92-99.5%) and secondly, the type of salts in solution. Membranes are very good at rejection high molecular weight compounds and multivalent ions. Monovalent ions such as Na+ and Cl- (Sodium and Chloride) are not rejected as well and are the leakage ions."

http://www.remco.com/ro_quest.htm

So, if that 10ppm remaining in the RO water is all sodium and chloride, is that too high a level? I can add a DI unit if needed, but if this level is not likely a problem, I won't bother.

TW
 

Tom Barr

Founder
Staff member
Administrator
Jan 23, 2005
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Re: My RO water still has 10ppm TDS - What is it?

10ppm is not much and given the starting water also.

Regards,
Tom Barr
 

Simpte

Prolific Poster
Feb 17, 2005
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Re: My RO water still has 10ppm TDS - What is it?

Temperature also plays a part in the units effectiveness. I believe R.O. units work best when the water temp is 78 degrees. Any hotter or colder and they don't run as efficient. Not the a degree or 2 will have any noticeable effect but you get the idea.
 

trcpdx

Junior Poster
Jan 24, 2005
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1
Portland, OR
Re: My RO water still has 10ppm TDS - What is it?

Tom Wood said:
My water starts as 510ppm, 24Gh, 16KH, that also goes through a whole-house salt-based water softener before being processed by the RO unit. The end result is 10ppm TDS.

Tom - how are you measuring? Just read something about the accuracy of TDS meters. Seems a meter with a range of 0-999ppm and a rated accuracy of +/-2%, might have an error range of +/- 20ppm. That 2% could be 2% of the full scale!
 

Tom Wood

Guru Class Expert
Jan 24, 2005
139
0
16
Kerrville/Austin, Texas
Re: My RO water still has 10ppm TDS - What is it?

Yeah, it's a cheapo TDS meter that I bought with the RO system, but it's the best I can do. I was really more interested in an order of magnitude feel for the end result anyway, rather than an absolute value.

TW
 

trcpdx

Junior Poster
Jan 24, 2005
17
0
1
Portland, OR
Re: My RO water still has 10ppm TDS - What is it?

Tom Wood said:
Yeah, it's a cheapo TDS meter that I bought with the RO system, but it's the best I can do. I was really more interested in an order of magnitude feel for the end result anyway, rather than an absolute value.

TW

So maybe your TDS is really zero! :)