Analytical chemist water

Source: reddit

Water is water is water, right?

No, as I've posted here before, not all water is equal. 

The above video distinguished among four water types found in this particular analytical chemist's lab.

First is tap water. That's the stuff that is piped into our homes and businesses from the local municipality. Generally, in the United States, it's pretty clean and safe to drink. Depending on where you are, however, it could have various dissolved ions in it because of the pipes and rocks that the water passed through on its way to the water treatment facility and onward to your house.

Second is deionized (DI) water. To produce DI water, tap water is run across resin beads what allow for ion exchange. The positive ions in the tap water are absorbed by the beads and replaced in the water with hydrogen ions (H+) and the negative ions are replaced with hydroxide ions (OH-). Eventually those beads have to be recharged as their capacity to absorb ions is finite. 

DI water is not the same as distilled water, though both are 'cleaner' than tap water alone. I have used both distilled and DI water in college and summer camp chemistry labs. Both are certainly good enough for the chemistry work that we do on a high school level.

Third is MillQ water, produced by a three-stage process which is already light years beyond anything I've ever used in a lab. The video voice describes it as 18.2 megaohm[·cm] which measures the water's resistance to current. The more dissolved ions (electrolytes) water has, the lower its resistance.

Fourth, she mentions LCMS-grade water means Liquid Chromatograph/Mass Spectrometry water. I'm already out of my depths to explain why this water is purer than the previous water much less the final water she mentions - Optima LC/MS water.

However, as the comments on the video mention, all of this is problematic because of how the various waters are stored - dissolved silicium from glass bottles or CO2 or plasticizers if stored in polymer bottles.