High Nitrates In Source & Makeup Water

Mark Taber · Jun 17, 2017

I run my water through an RO unit and then through 2 DI units however, as my source water is high in Nitrates I still see Nitrates in my make up water. Does anyone else have this problem and how do you overcome this?
I have replaced my RO/DI unit with a new one but still the same problem.

jsker · Jun 18, 2017

I would suggest, adding active carbon in stead of the carbon block filter. If the still dose not do the trick add another stage of carbon.

If I my ask, what do your nitrates read?

Randy Holmes-Farley · Jun 18, 2017

Mark Taber said:
I run my water through an RO unit and then through 2 DI units however, as my source water is high in Nitrates I still see Nitrates in my make up water. Does anyone else have this problem and how do you overcome this?
I have replaced my RO/DI unit with a new one but still the same problem.

IMO, it is highly unlikely that 0 ppm TDS water has enough nitrate it it to be important. Remember, you add massive amounts of N daily in foods.

Randy Holmes-Farley · Jun 18, 2017

DO you know your test kit is working right?

Mark Taber · Jun 20, 2017

Thanks for the responses. I have used 2 different test kits and my source Nitrates is between 30 - 50 and after running through RO/DI unit, I get it down to between 1 and 5. I am using 2 di units and 2 carbon blocks. I will try the plain carbon idea but who does this strip out Nitrates?

Randy Holmes-Farley · Jun 20, 2017

Carbon isn't going to bind appreciable nitrate, and that amount of nitrate, even if real (I'm skeptical, Ro/DI is effective at removing nitrate), is small relative to food inputs.

Foods might add on the order of 1-2 ppm nitrate daily, while topping off 1% daily with 2 ppm nitrate fresh water adds 0.02 ppm. That's a hundred fold lower and not significant (IMO).

Mark Taber · Jun 21, 2017

Interesting observation this morning. I checked the make up water and it read 1-2ppm Nitrates. I changed the DI resin in both canisters and it dropped to zero. I change my resin every 3-4 weeks so I will now do this every 2 weeks. I didn't realize that that amount of Nitrate can get past an RO unit and also, that resin can strip it out but can become exhausted very quickly.

Randy Holmes-Farley · Jun 21, 2017

Mark Taber said:
Interesting observation this morning. I checked the make up water and it read 1-2ppm Nitrates. I changed the DI resin in both canisters and it dropped to zero. I change my resin every 3-4 weeks so I will now do this every 2 weeks. I didn't realize that that amount of Nitrate can get past an RO unit and also, that resin can strip it out but can become exhausted very quickly.

What is the TDS drop from the membrane? Maybe it is not functioning properly (e.g., has a hole in it).

Nitrate should drop by more than 90% going through an RO membrane.

Mark Taber · Jun 21, 2017

I will check once back from my holiday. This is the second RO unit I have had so it would be weird to have on both
When I am back I will test the water at each stage so this will give me an idea what is and is not stripping out Nitrates.
Thanks for the tip