As stated by others, the original post if full of falsehoods. There are also falsehoods in the replies. I have a lot of experience with ultrapure water, my company makes very large ultrapure and bench top labwater systems.
1) UPW (ultrapure water) is not caustic. Conversely, in it's purest form it because acidic when exposed to atmosphere because it readily absorbs CO2, which converts to carbonic acid. However, by default, UPW can only have a pH of 7 (again when not exposed to air). So proper pH measurement can only be done inline or with proper buffers. We actually wrote a paper on this topic because researchers were always complaining that their water was acidic.
2) UPW will corrode iron, brass, poor quality steel. However, it will not corrode stainless steel as long as the welds are proper, even then hard to make SS conducive to corrosion by UPW. Example, resistivity meters that we use are made from SS (need to be to conduct electricity across 2 metal probes to get a reading).
3) UPW will not corrode Pyrex as stated above. After all, HPLC and LCMS grade water (not going to define so look it up) is placed in glass containers. Distilled water is even made in glass stills for laboratory use. Having said this, it will leach some silica and boron, so they actually should use special glass. But it won't corrode it. I had a bottle of LCMS grade water sitting in the lab for years. Also, exotic plastics don't need to be used, such as PFA, PVDF, Halar, etc. The possible exception is in a fab of a semiconductor plant. We use polypropylene, PEX (cross-linked polyethylene), and even PVC (but not ideal because in some cases the glue can leach TOC's - total organic/oxidizeable carbon that are undesireable, for example in a waste water treatment plant.).
4) the comment that "pure water is less corrosive than water with impurities", is not completely true. Put a brass or iron bolt in distilled water and see what happens compared to tap water. Also, power plants don't use UPW because tap water is more corrosive. All steam powered plants (coal, gas, nuclear, etc.) use UPW, because residuals will form on the turbine blades and throw them off balance and destroy them. Also, impurities from the water will leave residue on the evaporators in the cooling towers and render them useless. One can't compare the corrosiveness of tap water and UPW. I've seen very corrosive tap water (classic example is the city water issue in Flint, MI. The water is corroding the pipes and leach lead into the water because it contains chlorates). UPW can be corrosive to other metals because it forms carbonic acid when exposed to air. etc......
By definition, ultrapure water is defined as ~17.0-18Meg-ohm or type I water. Meaning does not contain dissolved ions to conduct electricity. In theory, if you throw your TV into a tub full of UPW it won't short out. If swimming in a lake of UPW and lightening hits the water you won't be electrocuted, because it contains no ions to conduct electricity. The theoretical limit for UPW is ~18.26 Meg-ohm.
DO NOT DRINK UPW, it will corrode metal fillings, leach calcium from your bones, eat the enamel in your teeth, even can cause your cells to explode (due to osmosis). Fortunately, before you can do to much damage you likely will feel sick to the stomach. The irony is that the purer the water is the worst it is for you to drink. Though, you can denature UPW by mixing it with Tang, powdered drink mix, tea, coffee, etc. It will make very strong tea and coffee. Even though distilled water is not considered UPW (by definition, it is a low grade Type II), it isn't good for you to drink because it has no minerals. Also tastes insipid. While on the subject, home RO or 'purified water' you buy in the store, is considered as ASTM Type IV, but in our industry we call it Type III.
Yes, UPW is one of the strongest solvents known to mankind. But that doesn't mean it will eat through everything. It just means it's always trying to reach equilibrium by leaching out ions, VOC's and CO2.