RO/DI TDS Reading

OK I checked my ro/di's tds and it's weird. My waste from the ro/di is 128, the filtered is 5 and I checked my tap water and it's 90.. I find it strange that the waste water on the ro/di is higher than my tap. shouldn't it be pretty close to the same since it's the same water going in?

 

When was the last time you changed out the filters? Luna

 

RO/DI should always be zero.

Is your refractometer calibrated right? With tapwater at 128, I wouldnt even bother with a RO/DI.

 

Waste water has a higher concentration of the elements that you are taking out of the tap.

 

Dec 2007 I changed the filters I might make 3 gallons every other day with it. It takes forever and there is always so much more waste water than filtered. Why is that? It fills up a 7 gallon bucket with waste, while the filtered is only at like 1/3 full...... Geek you think 90-128 is ok to use fresh?


My filtered has never been 0 even with new cartridges

 

That's the way RO/DI works. Think of it this way;

5 gallons at a TDS of 90 goes in
1 gallon at a TDS of 5 comes out.
Since the filters work by Osmosis, there's only one place for the extra dissolved solids (and remaining water) to go....to the wastewater. That's why

 

that's strange Inwall but I understand. good explanation! thanks!

 

Keep in mind that the sediment, carbon and DI filters should be changed out every 6 months. The R/O membrane can be replaced every 1 1/2 to 2 yrs. I have a 4 stage R/O unit that was giving me the same result as you(5ppm) and never reached a zero reading until I added a DI stage. Now I have a zero ppm reading every time. Just a thought. Luna