TBH, I sill doubt it was the water. After that water has been sitting for several days, you'll get some evaporation and with the small amount you probably had you're likely to get a high salinity reading. Mixing you're own however is never a bad idea. I used to get it from my LFS because I live in an apartment and thought it would be too much to make my own. I got an aquatic life 4 stage twist in RODI and was able to fit it under my sink easily. I believe the 3 stages are $110 and 4 stage is $125 for a 100GPD.