RO/DI Water & Phosphates

[Dwb859]

I just did a test on my RO/DI water and got a phosphate reading of 0.02 ppm PO4 using a Milkwaukee pro meter. MY source water has a TDS of around 125 ppm and out the DI it's 0.2 ppm TDS. I know a RO/DI doesn't remove 100%, so wouldn't it make sense to have a slight trace of phosphates in RO/DI water? Especially if you are using a accurate meter? All my cartridges are a couple months old, RO Membrane is 8 months old. I know many peoples TDS meter doesn't read a decimal and could appear that you have 0 TDS water when you actually have a very small amount that the meter can't detect.

[cap032]

My source water is 120-125 tds as well. Its 1-2 after RO and 0 after DI. It sounds like either your RO membrane isnt functioning properly or your DI is exhausted if you arent getting 0 tds water after DI. Others get 0 water with much higher tds than us.

[Dwb859]

Originally Posted by cap032

My source water is 120-125 tds as well. Its 1-2 after RO and 0 after DI. It sounds like either your RO membrane isnt functioning properly or your DI is exhausted if you arent getting 0 tds water after DI. Others get 0 water with much higher tds than us.

I've talked to the RO/DI company and was told that a RO membrane should be removing at least 90% of the tds for the membrane to function properly. After the DI, something like 99% of the TDS should be removed, not 100%. Going by that, it would seem impossible to get a true reading of 0.00 ppm TDS out of a RO/DI unit. I've seen many peoples TDS meters and they all test 0, 1, 2, 3, etc....I had one that test 0 until I got a more accurate meter that can detect 0.1 ppm TDS.

I've gotten the 0.1-0.2 ppm reading even with a new DI, my membrane seems fine. My unit even performs a membrane flush to prolong the life of the unit.