RO Question

Chrisz · Jan 5, 2012

I did not notice until today but my TDS monitor on my R/O system was reading 10.

I replaced the first sediment filter and it went back to zero, can I use the water that read 10?

My R/O filter is a Kent Marine Deluxe Maxxima Hi-S RO Unit.

AZDesertRat · Jan 5, 2012

Sediment filters have very little to absolutely nothing to do with TDS, they remove suspended solids, things in the 1 or 10 micron range. TDS or dissolved solids are in the 0.0001 micron range, down at the atomic level.

You change your sediment filte rand carbon block EVERY 6 MONTHS to protect the RO membrane from particulates, sediment, silt, colloidal materials and chlorine. The RO membrane is the workhorse of the system and removes 90 to 98% of the TDS or dissolved solids, not suspended solids and the DI resin removes the remaining few percent.

What is your tap water TDS? RO only TDS and RO/DI TDS if you have DI which you should? Calculate the rejection rate or removal efficiency of the membrane to determinw how well the membrane is working and to determine if it is in need of replacement. Tap water TDS - RO TDS / tap water TDS x 100 = rejection rate.
If its less than say 96% it may be time for a new RO membrane and definitely time to add a DI filter.

Chrisz · Jan 6, 2012

It has been about 4 months since I replaced the carbon filter and I have never replaced the other 2 filters, it is probably time. I will try to figure out what the out put of the good and bad water is. I know for sure that I am putting out about one gallon of good water in 99 minutes at 65 psi, I have the RO unit on a sprinkler timer instead of a float sensor.

Can I just test the water coming out of the RO unit to see how it is performing, PH, Phosphate and silicates? I am on well water so there will not be any additives to worry about.

So what is the TDS meter for?

OOPS I missed the boat on your formula, I will check both tap water and RO water with the TDS meter and see what I got.

AZDesertRat · Jan 7, 2012

You cannot accurately test RO or RO/I water with hobbyist test kits since they are not designed to test ultrapure waters and wil not have any level of accuracy at all.
The TDS meter is how you test the purity of the treated water, its really the only way short of expensive lab grade equipment. The TDS meter tests the conductivity of the water since about all contaminants are electrically conductive.

Chrisz · Jan 8, 2012

Thanks, I am not sure why when I replaced my sediment filter the TDS meter went to zero but it is back 10. I guess I need to replace the filters, it has been 2 years for the last 2 filters. I was waiting for the DI resin changing color stuff to change color but it never did, is this the color it is suppose to be when exhausted?

AZDesertRat · Jan 9, 2012

Color changing resins are a very poor indicator of resin condition, I always depend on a handheld TDS meter for accuracy. Resins can change in streaks, top to bottom, bottom to top, all at once , never, etc. Its almost always too late when it does turn and you are passing concentrated contaminants by that time, especially weakly ionized things like nitrates, phosphates and silicates. Use your TDS meter always and I wouldn't even waste money on most color changing resins, they actually contain dyes which wash off and register as TDS.