[mike31154]

How many stages does your set up have? The most basic way to run it would be a carbon stage & the RO membrane. The carbon stage removes chlorine which would destroy the membrane. In most cases at least one sediment filter is used before the carbon stage. This will keep the undissolved crud from clogging up your carbon stage. Sediment filters are cheap & come in many different micron ratings, so you can try a few different ones to see how they perform with your water. Solid block carbon stages will also have different micron ratings, so be aware of that. Also check to see if Yellowknife uses chlorine or chloramine to treat the tap water. If they use chloramine, you may need two carbon stages. My system came with a carbon block & a refillable carbon stage. I removed the refillable one years ago & now run two sediment filters of different micron ratings in front of the solid carbon stage.

If you have a DI stage, you may as well use it. With TDS as low as yours, the RO membrane itself should bring the TDS to 1 or 0 before the DI, so the DI media will last for years. Having the DI in there will help ensure that any remaining bad stuff is stripped from the water. Even with my set up (75gpd membrane) and incoming TDS of 210+, the RO membrane manages to get the TDS down to 0 before the DI most of the time. It seems to get to 0 faster in the cooler season (within 5 minutes) when the incoming water temperature is around 8 degrees C. I suspect your incoming water in Yellowknife is fairly cold as well. In my experience that works to your advantage in terms of TDS coming out of the membrane. Downside is, slower production.

When it comes time to replace your RO membrane, you might consider switching to a 75gpd. Production will be a little slower, but 75gpd is better at removing TDS than 100gpd. You'll need to replace the restrictor as well to match the new membrane. Again, with your low incoming TDS, you could tweak the waste water flow after your restrictor by adding a small ball valve & restricting the waste water further. Need to be a little careful about that, since you will be forcing more water through the membrane with the higher restriction & that may impact membrane life. The advantage however, is better good to waste water ratio & faster production. Incoming water pressure will also have a significant effect on how well, or poorly your system performs.