TDS results for a 4-stage RO unit?

[d3rryc]

I've got a 4-stage Aqua-Pure undersink RO unit that's rated for 25 gpd. The stages are:


Five micron sediment & rust filtration
Activated carbon filtration
Reverse osmosis membrane
Final activated carbon polishing filtration

What kind of results should I be able to expect in terms of final TDS? FWIW, my TDS going in is about 250.

[justahobby]

I'm getting 0 TDS with 75 gpd from buckeye.

[d3rryc]

From a 4-stage?

[corydrysdale]

I would think no matter how many stages you have on a RO/DI unit your final TDS should be 0

If this is the case then its fine. If you start to show something else then 0, then it may be time to start changing your filters. Mine is rated for 75 gallons a day and after running maybe 1000 gallons i showed 1 on my TDS output. I have a 6 stage unit, using a pressure pump maintaining 75 psi.

[SABOB]

Without a DI stage,probably won't get 0 TDS. You can figure out what you should be getting based on rejection rate of your RO membrane (usually 95% to 98%)

[corruption]

Drinking water (typical under-sink units) and RO/DI are very, very different -- the demineralization of the water makes the RO/DI water very caustic... it will osmolate minerals out of your teeth -- not what you want to drink :)

On the other hand, typical drinking water RO units produce somewhere in the range of 15-60ppm, assuming the filters are all in good working order, and based on the rejection rate of your RO membrane.

-Justin

[Big_Pun]

you could make it a 5 stage and it will last you a while just add a GAC filter as the last filter before the ro filter and dump the final carbon polishing filter and add a stand alone di resin filter, or you do like i do i have a T fitting between ro and di and a valve to cut off the di and you can put the polishing filter there and make drinking water

[justahobby]

4 stage with a 5 micron filter. The first few gallons were around 1-2 tds. I actually measure with a PWT which is insanely accurate....... Measures in micro siemens and my finals reading is 0.01 micro siemens. I'm glad I went with buckeye :)


From a 4-stage?

[d3rryc]

Mine's a 4-stage with a 5-micron filter as well, but my TDS coming out is still 20. I replaced both filter cannisters AND the RO membrane just yesterday, hence my question.

[justahobby]

Are you using the waste water by chance? Cheap filter? Meter not calibrated?

[d3rryc]

I don't see how I could be using the waste water - it runs from the RO membrane to the drain via the air-gap valve. The new filters and RO membrane are Aqua-Pure branded, not cheap knockoffs, so quality should be solid there. The inline TDS meter is brand new and factory calibrated, with the results corroborated by my hand-held TDS meter.

[link]This (http://www.aquapure.com/sysproducts/bigro5500.html)[link] is my RO unit. How and/or where could I insert a DI stage given what I have to work with?

Justahobby, just out of curiosity, what's your incoming TDS?

[BIGBIRD123]

In your description your set-up, there is no mention of DI. If you are not using DI, then you will never read 0. I would somehow add a DI cartridge to the end of the set-up. I have an extra DI cartridge and resin you are more than welcome to try. My in-coming TDS is 265 and out is 0. I use a built-in TDS meter and a hand-held.

[d3rryc]

Thanks, BigBird. I'll PM you for details.

[SoLiD]

In your description your set-up, there is no mention of DI. If you are not using DI, then you will never read 0. I would somehow add a DI cartridge to the end of the set-up. I have an extra DI cartridge and resin you are more than welcome to try. My in-coming TDS is 265 and out is 0. I use a built-in TDS meter and a hand-held.

+1
Steve hit he nail right on the head.

[Roo&Lis]

You say inline TDS meter. Does the meter happen to have an in/out switch. I thought I had a high TDS till I figured out I was looking at what was coming in rather than out.

[BIGBIRD123]

yes, the in-line has an input reading and an out-put reading. I then check with my hand-held to be sure.

[Bill S]

Drinking water (typical under-sink units) and RO/DI are very, very different -- the demineralization of the water makes the RO/DI water very caustic... it will osmolate minerals out of your teeth -- not what you want to drink :)

On the other hand, typical drinking water RO units produce somewhere in the range of 15-60ppm, assuming the filters are all in good working order, and based on the rejection rate of your RO membrane.

-Justin

Justin, I almost always agree with you. But this one is an urban legend. Distilled water (and distilled spirits) are harmless. This has been the subject of a lot of quack medicine over the years. Mostly from people hawking their own products.

[CoryDude]

You could always get an add-on cannister of di resin. Buckeye has them along w/refillable resin cartridges.

I can get a better rejection rate from my tfc membrane w/h2o pressure between 60-80 psi.

[corruption]

Justin, I almost always agree with you. But this one is an urban legend. Distilled water (and distilled spirits) are harmless. This has been the subject of a lot of quack medicine over the years. Mostly from people hawking their own products.

No worries, Bill -- always glad to be schooled with new information! :) I've already got a drinking RO system and separate RO/DI system, so its a null point for me... i like a little bit of mineralization for cooking my pastas, adds flavor! :D

-Justin

[BuckeyeHydro]

I've got a 4-stage Aqua-Pure undersink RO unit that's rated for 25 gpd. The stages are:


Five micron sediment & rust filtration
Activated carbon filtration
Reverse osmosis membrane
Final activated carbon polishing filtration

What kind of results should I be able to expect in terms of final TDS? FWIW, my TDS going in is about 250.
As mentioned above, yoour RO membrane should reduce your feedwater tds by more than 90%. So with 250 ppm going in, the water coming out of your RO (before it goes through the final taste and odor filter, should be less than 25 ppm. That final taste and odor filter will actually add tds. If you don't have a pressurized storage tank, get rid of that final filter stage.

Russ

[BuckeyeHydro]

BTW - DI water IS very aggressive - it will corrode through copper pipe for instance. Don't run Ro water through copper fittings/pipe either. The lower the TDS, the more aggeressive the water. Use only plastic fitting/pipe/tube.

Russ