Does Reverse Osmosis water contain any ions at all?

hokenfloken · May 29, 2010

Greetings! I've been searching the forum for awhile now and I cannot find any definitive answer to this question.

I currently build my water from distilled water and brewing salts. I would like to start using RO water due to the lower cost.

Can I expect RO water to be nearly free of salt ions?

Any experienced advice would be greatly appreciated. Thank you very much.

Special Hops · May 29, 2010

http://en.wikipedia.org/wiki/Reverse_osmosis

hokenfloken · May 29, 2010

Thanks for the wikipedia link, although I have read it already. I guess my question whether or not any of the salt ions are smaller than 0.1 nm. If they are larger, they will be filtered out. If not, they will pass though, or at least that's my interpretation. If RO water is essentially free of ions then what is the point of distilled water? Thanks.

artbrau · May 30, 2010

I believe distillation and RO are two different processes that get you to the same place.

remilard · May 30, 2010

hokenfloken said:
Thanks for the wikipedia link, although I have read it already. I guess my question whether or not any of the salt ions are smaller than 0.1 nm. If they are larger, they will be filtered out. If not, they will pass though, or at least that's my interpretation. If RO water is essentially free of ions then what is the point of distilled water? Thanks.

RO doesn't exclude particles solely on the basis of size, so your interpretation isn't quite correct.

The answer to your question is that the water will not be ion free, there will be lower ion content than there was before, it will probably be very low (single digits ppm for each ion), and it is impossible to predict exactly what it will be.

Hoppocrates · May 30, 2010

A member of my home brew club sent the supermarket RO refill station water to the lab. It was surprisingly incredibly efficient and nearly distilled. You can see the results at the bottom of this page:

http://www.thirstyhomebrew.org/

bad coffee · May 30, 2010

IF you're using RO-DI (DeIonized) water it should be 0 PPM. If it's just RO, then it will depend on the membrane.

(From my aquarium knowledge)
A 100GPD (Gallon per day) filter has a 90% rejection rate.
A 75GPD has a 97% rejection rate.

So depending on the membrane, you might be getting really good water or just good water. YMMV.

B

GreenMonti · May 30, 2010

I have a RO/DI unit for my reef aquarium. Every time I fire it up I hit the TDS meter to check my incoming and outgoing TDS rate. Since day one I get 0 PPM on the outgoing.

The above post about the membrane is correct. I also believe the quality of the membrane has to do with its rejection rate.

Does Reverse Osmosis water contain any ions at all?

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