What makes it through an ro membrane?

[Cory]

Im curious, what generally can get through a reverse osmosis membrane?

I know silicate does, but what else?

My ro system brings down 600ppm to 8-16ppm iirc. Its about 98% rejection. But i wonder what get through.

 

[Killer Karma]

Short answer - any particle smaller than the pore sizes on your individual membrane or that does not "stick" to your individual resins. Specifically what things would be very difficult to determine as it would be based upon what is in your water. I'm on a well system so it is different than "city tap" water which could be filled with all sorts of stuff. You are in Canada but here in the states there is chloramine, flouride, and other stuff added to the water. Further due to our dependence on so many pharmaceuticals even our ground water is filled with remnants of them. Then there is the alarming presence of Glyphosate being noticed in many bodies of water. I'm sure you could send a sample to a certified lab and get a fairly comprehensive overview of the remnants.

 

[Randy Holmes-Farley Verified Community Expert]

Im curious, what generally can get through a reverse osmosis membrane?

I know silicate does, but what else?

My ro system brings down 600ppm to 8-16ppm iirc. Its about 98% rejection. But i wonder what get through.

All smallish molecules get through, especially uncharged ones. The smaller they are, the more they get through. Silica gets through as silicic acid, Si(OH)4.

Charged ions are effectively larger because of a tight sphere of 4-12 hydrating water molecules tightly attached to them.

 

[Cory]

Short answer - any particle smaller than the pore sizes on your individual membrane or that does not "stick" to your individual resins. Specifically what things would be very difficult to determine as it would be based upon what is in your water. I'm on a well system so it is different than "city tap" water which could be filled with all sorts of stuff. You are in Canada but here in the states there is chloramine, flouride, and other stuff added to the water. Further due to our dependence on so many pharmaceuticals even our ground water is filled with remnants of them. Then there is the alarming presence of Glyphosate being noticed in many bodies of water. I'm sure you could send a sample to a certified lab and get a fairly comprehensive overview of the remnants.

We get all that too. My city water is well water.

 

[Cory]

All smallish molecules get through, especially uncharged ones. The smaller they are, the more they get through. Silica gets through as silicic acid, Si(OH)4.

Charged ions are effectively larger because of a tight sphere of 4-12 hydrating water molecules tightly attached to them.

Im still curious whats in my 10ppm ro water, because I dont know whats big and small. Is it even necessary to use deion resin?

 

[chipmunkofdoom2]

Im still curious whats in my 10ppm ro water, because I dont know whats big and small. Is it even necessary to use deion resin?

Per Randy's article on RO/DI systems, the DI resin is responsible for removing phosphates and copper. I wouldn't go without it for that reason alone.

 

[Cory]

Per Randy's article on RO/DI systems, the DI resin is responsible for removing phosphates and copper. I wouldn't go without it for that reason alone.

Great! I didnt know Randy wrote about this. Time to read. Thanks

 

[Randy Holmes-Farley Verified Community Expert]

Im still curious whats in my 10ppm ro water, because I dont know whats big and small. Is it even necessary to use deion resin?

Here's a table of the rejection rates for a bunch of things for you to gauge:

http://www.purewaterproducts.com/articles/ro-rejection-rates

 

[Cory]

Here's a table of the rejection rates for a bunch of things for you to gauge:

http://www.purewaterproducts.com/articles/ro-rejection-rates

It seems i should be mainly concerned about ammonium, nitate, boron, cyanide, potassium, arsenic, sodium and chromate getting through, no? Everything else is has a fairly high rejection rate. Nitrate im not worried, boron not much either as they are both relatively harmless. But ammonia could be a concern. But even if small doses of ammonia enter, really it shouldnt do much in such small quantities right?

Would you add water conditioner to ro only water?

 

[Randy Holmes-Farley Verified Community Expert]

It seems i should be mainly concerned about ammonium, nitate, boron, cyanide, potassium, arsenic, sodium and chromate getting through, no? Everything else is has a fairly high rejection rate. Nitrate im not worried, boron not much either as they are both relatively harmless. But ammonia could be a concern. But even if small doses of ammonia enter, really it shouldnt do much in such small quantities right?

Would you add water conditioner to ro only water?

The concern relates to what is there also, and how much of a concern it is.

97% rejection of 1 ppm copper leaves 30 ppb. That might be too much.