Is zero tds possible with RO only?
 

I'm in Calgary btw. My dual stage meter shows the source water to be about 280 (though I just dipped the inline probe in a glass of water to avoid making more cuts in my pipes to make sure the meter showd anything other than 0). I'm getting a reading of 0 without running DI. The unit has 5 micron sediment, 5 micron MATRIKX CTO/2 carbon and then dow filmtec 75 gpd membrane.

With 98% rejection rate I was expecting around 280 x 0.02 = 6 or so

When I first set things up btw I was getting a reading of 1 after the RO but after 10 min or so it read 0.

Yeah it's possible the DI actually does very little, will usually drop the TDS by around 10ppm at most. I've setup RO systems in Calgary before and got 0 without the use of DI.

280 does seem awfully high for Calgary though, but it could just be your location. It likely depends on what kind of solids you're dealing with, perhaps the pre-filters are doing a lot of the work prior to it hitting the RO membrane. It would be interesting to compare TDS before and after the pre-filterers.

Hmm, my source water shows a TDS in the mid 200's as well and my system is similar to yours, 75 GPD. RO TDS gets down to 1, occasionally 2, but I've never seen it at 0. Source water comes from a local lake and it's considered somewhat 'hard' due to the makeup. I've checked my source water both with the Dual TDS meter and a cheap handheld. There's a discrepancy of about 30 to 40 with the Dual meter having a higher reading than the handheld for source water TDS. I'm inclined to put more trust in the Dual meter, since I used both probes and they were within 1 TDS in their readings.

Did you check the source water with both probes? If not, might be worthwhile as a comparison and to instill confidence in the reading, although an accurate reading at a TDS of 280 does not necessarily translate into an accurate reading at the lower end of the scale. That certainly seems to be a concern with refractometers in many posts & threads. Pretty sure the Dual TDS meters have a calibration adjustment on them, so it may be an idea to look into that.

Or, maybe the makeup of your source water is such that the solids are readily separated, who knows. Hopefully some fellow Calgarians will check in with their experiences.

Brett, I always get readings of 0 to 1 ppm using R/0 only. Mind you our water is pretty good; 16 to 20 right out of the tap.

Whoa 16 to 20! Your membrane will last a lifetime lol.

The meter I think is much more acurate with water flowing past the probe contacts. Like I said I only dipped the probe into a glass of tapwater so there was no flow. The unit is not quick conenct fittings so I *really* didn't want to bother with making another cut and then redoing the connection later.

I'll Continue as is for now since it seems that things are ok. I'm sure these meters are not THAT accurate but whatever I'm getting out is very low in tds compared to the source. Good enough right now I need SALTWATER!

YES you/we do!

Re: water.

I'm at 5" right now. My wife tells me that's not gonna cut it.

ONWARD!

[quote=lastlight;460267]

I'm at 5" right now. My wife tells me that's not gonna cut it.




Hehe Does she wear glasses? If so, switch out the lenses to macro. :mrgreen:

^^ She doesn't like the shallow look? :lol:

As for the question.. up here in the NW, I'm only running RO, and as of today, I am getting 130 IN... 0 OUT... that's on a 7-8month old membrane.

Looks like you have your answer already but since this is a topic I feel I have a tiny bit of knowledge on, I'm compelled to post anyhow.

Yes 0 TDS is possible in Calgary water with RO alone, but typically it's better still to use the DI because there tends to be TDS surges and the DI will catch those. It depends on the membrane, some brands have better rejection rates than others. With the membrane I have right now, the best I can get after a 20 minute flush is about 3-4 TDS (it will go down to zero after about an hour or so). The membrane I had before had such a great rejection rate that it would be zero TDS within a 2 minute flush. I've kept my old one so I can remember what kind to order when I've had enough of this one.

Keep an eye on your RO output TDS, when it stops going below 10 on a 5 minute flush it's pretty much time to let it go. Expect to replace them around 12 to 18 months around here.

If you don't have a flush kit, get one.

And and whatever you do, even if you have a auto-shutoff on your RO, don't hook it up to a float valve or float switch in your tank, because constant on/off's are the fastest way to kill a membrane. They are designed for long runs, so turn it on, flush it for 2-5 minutes or whatever, then let it run for say 12 hours. Shut it off and leave it off until you need more again.

The ONLY thing those shutoff kits should be used for is preventing overfills. As soon as whatever it is you're filling is full, turn off the source water.

Lance and JDigital that is GROSS. I've taken slight offense guys...just a casual warning but please keep my threads on-topic and clean.

Yeah on my last tank I ran the ro/di straight to a float valve in my tank and battled algae like you wouldn't believe. Bet it was the creep. I have to install a float into my water-change top tank after I can pull the ro/di line out of the display.

I actually cut the autoshutoff stuff out of the unit as they are cheap and always fail. I bought a backup but the creep issue drove me to get rid of it altogether and besides the float valve in my reservoir I also have it plumbed with an emergency drain. I am buying an electronic solenoid and putting it on a timer to run for a set period of time nightly. Right now it's on full-manual. Meaning I gotta keep an eye on it!

The unit had a flush kit but since my old unit didn't have a flow restrictor I didn't even know what it was. When I had issues getting the thing to not dump waste water like a banshee I realized what I had removed and put it back in place. I need to add a new valve in to do flushes still.

[quote=lastlight;460290]Lance and JDigital that is GROSS. I've taken slight offense guys...just a casual warning but please keep my threads on-topic and clean.


My apologies. :redface: I misinterpreted your post, thought it was a joke.

WRT the auto shut off valve, I haven't been able to get mine to work properly at all either and would never trust the thing. After some small mishaps, I only run the system manually and set the timer on the kitchen stove to remind me to check it periodically. No way I'd leave the house with the system running.

Lance you silly arse!

I was kidding. Seriously man! Have I not established sufficient levels of silly to make that obvious? Dammit!

Now that's a lot cheaper than the solenoid which could still fail. I'm doing this. Even if I somehow don't notice the stove going off my wife will!

Well, it did kind of surprise me. :surprise:: Thought maybe you got up on the wrong side of the bed this morning.
Back to topic: Brett, I use the BRS top-off valve as well as a timer from Rona. I figure this ensures no accidents and will cover my silly arse.

Dude when you're filling a tank that's been 1.5 yrs in the making there is no wrong side of the bed. If/when I battle algae again...well then look out!

I likely will try and connect the new shutoff valve i bought if i can remember how just to waste a little less water when I ignore the stove alarm a few minutes.

Obviously not! I didn't have "gross" thoughts when I made my post.. :lol:

Oh crap. Looking back you DIDN'T have any gross thoughts. Haha just Lance and I.

But seriously guys...howzabout that tds?

wow, there is quite a variance in the water quality in the City. I checked mine last night and I got 125 out of my tap (in Riverbend).

K.

I'll bet if I had the probe installed properly and not just placed in a cup of water it'd be lower.

Really, 125 in Riverbend eh? I would not have thought it but then you're off the Bearspaw reservoir and not Glenmore (figured the separation line was further south than that, but maybe not.) Water from the Bow seems to be low 100's, water from the Elbow is high 100's to mid 200's (seems to fluctuate).