RO membrane damaged or not?

Oceanbear1 · Mar 5, 2015

So long story short, I moved to Colorado and put my rodi unit in my garage and forgot about it. I am running a much smaller system now, so I had just been buying fresh water from the local store. I decided to get it out this weekend and realized everything had frozen(detached garage), so I bought new filters and a new membrane. The new membrane didn't fit, so I decided to plug my old one in just to see what happens. After letting it run for about an hour I got a TDS reading between 2 and 3 ppm before the DI.

So.... Given the Tds reading, is it safe to use still?

CuzzA · Mar 6, 2015

As long as your TDS meter is calibrated and reading accurate 2-3 output sounds like it's functioning properly.

AZDesertRat · Mar 6, 2015

There are couple of Indicators.
What is the tap water TDS going in and the RO only TDS? Use these two numbers to calculate the rejection rate, tap TDS - RO TDS / tap TDS x 100 = rejection rate so say you have 100 tap TDS and your 3 RO only, 100-3=97, 97/100= 0.97, 0.97x100= 97% rejection rate.

The other indicator is the GPD. Usually when a membrane freezes it ruptures or tears so water leaks through with only partial treatment so the GPD goes up. If it is a75 GPD RO membrane and you are seeing more than 3 gallons per hour at 50 psi inlet pressure and 77 degree water it is bad. You probably have water colder than 77 degrees so it should be even less than 3 GPH.

Also, what are you testing he TDS with? Is the calibration good and is the meter ATC temperature compensated? If it is an inline meter, they are not ATC so any difference between water temperature and air temperature will give you a skewed reading, where a good $25 ATC handheld will be much more accurate. With an inline it is a good idea to swap the probes every so often to make sure they agree or are close.