Warning for RO-only users

[gregzz4]

Nothing to panic over, but if you use a shut-off float valve on your RO holding tank ( as I do ) to shut off your system when the HT is full, this may apply to you ...

A few weeks ago I tested my HT water and found it to be a crazy 6PPM
That's nearly my City Water value

I washed out the drum (HT) and refilled it with a fresh run of 0 TDS from my RO only system. Since then I've topped it off a couple of times, so I've gone through approx 50g ? Doesn't matter
I tested the water in the drum this last weekend and found 2-4 TDS, depending on how the probe was positioned. I think these inline ones are sensitive to us ( interference ). Anyway , WTfudge

After some reading, and a bunch of PMs with 11purewater about Permeate Pumps, the cause and solution came about

Turns out that, because I use a float valve to close my RO water to the drum when it's full, the back-pressure on the Membrane kinda overwhelms it's ability to give me 0 TDS
What's happening is not really important. How it happens is

As the valve starts to close, it puts back-pressure on the Membrane and the TDS starts to climb
However long it takes for the valve to close is beyond me as I'm never around when it happens
Also, I have no idea what the TDS is when it's finally closed
But, I can tell you it must be very high. High enough to turn 45 gallons of 0 TDS RO water into 3-4 TDS crap

To confirm this, I ran a simple test tonight ( Thanks for the idea Andy )
I have an inline shut-off ( manual ) valve to my drum, and a Tee with another valve ( also manual ) that goes down the drain
I ran the system down the drain until I had 0 TDS. Then I opened the inline valve to the drum and closed the valve to the drain
Now the drum is being filled with 0 TDS RO water
Next, to simulate the float valve closing, I started closing the inline valve a bit at a time and, once it started to drip 4-6 drops/second, the TDS coming out of my Membrane started to climb
Who knows what kind of TDS I've been getting before the float valve in the drum is fully closed, but, as I stated above, it has to be HUGE to turn 45 gallons of 0 TDS RO water into junk

Suffice it to say I am going to revamp my system
I'll start by removing the float-shutoff valve and let the excess RO go down the drain until I shut off the water supply manually

In the near future I'll come up with a better way to turn off the system once the drum is full, but at least for now I found out where my TDS is coming from

And before someone jumps in and tells me to use a DI canister ...
I don't need one for my city water, so I'm not adding one just to solve this issue

[Slick Fork]

I've read before that RO systems really don't like the on/off cycle and do much better if you can do larger batches at atime rather then a litre here and a litre there.

I fill my top off container once every week and a half. A little more labour intensive, but I feel it's better for the RO membrane and better for my piece of mind as there's only a finite supply of water that could go into my tank if there's a malfunction.

[dino]

i think big batches is a better way to go also i just use my float as a back up if i forget to turn it off

[gregzz4]

Just to clarify ...

I don't leave the system running
When the drum gets low I purge the TDS creep, fill the drum, turn off the inline valve to keep the membrane pressurized, and then turn off the water supply

[Zoaelite]

A few weeks ago I tested my HT water and found it to be a crazy 6PPM
That's nearly my City Water value

My advice is to sit back and not worry about it.

Calgary water standard is between 156- 299ppm, I don't believe we are getting anything close to zero out of our units. As people have run successful tanks with Calgary water I don't think 6ppm of TDS is going to hurt you at all.

[kien]

Originally Posted by Zoaelite

My advice is to sit back and not worry about it.

Calgary water standard is between 156- 299ppm, I don't believe we are getting anything close to zero out of our units. As people have run successful tanks with Calgary water I don't think 6ppm of TDS is going to hurt you at all.

I didn't want to be the guy to say it but ya, freaking out at 3-5ppm TDS ?? You West Coasters are spoil by youre clean water! LOL. I don't panic until my RO reads 10tds at the exit. I try to replace filters sooner but sometimes I get busy (lazy) and don't notice until around 10 tds.

[Seriak]

But thank you for the explanation as it now tells me why my RO water is testing higher in my containers.

[kien]

Originally Posted by Seriak

But thank you for the explanation as it now tells me why my RO water is testing higher in my containers.

tru dat! I did wonder about that actually.. now we know!

[lastlight]

Really interesting on the float valve creep that's a new one to me. I just set a timer on my phone and manually shut things off (after a back flush) so I guess I'm not experiencing this fancy new creep.

[Madreefer]

Hey Greg the same thing happens to my water.
It's no big deal at all. I have a Vertek Puratek unit and after a few days of it not producing water for my reservoir the TDS has gone up to 44-45.
Been like that from the day I got it and it's a been a few years. I'm thinking in my case though it's just the watwr that sits stagnant in the line that the TDS meter is attached to. Besides your in B.C. we have great water.