Yes! DI Water really isn't ideal for drinking - that being said, it won't kill you to drink it either. The issues with drinking DI Water are the exact reasons why we want to use it for brewing! There are no minerals in the water. The water is hungry for minerals - water is a solvent and likes to break down things when it is not saturated with minerals. Issues with drinking DI Water:
1) Your teeth enamel can be stripped from the pure water.
2) It taste terrible - water has taste because of the minerals in it, DI Water taste smooth - almost vodka like without the burn. Thats why any "Purified water" always has "minerals added for taste" it is not truly pure, was just purified for them to clean/disinfect and re-profile the water.
3) Can't say I am an expert on this one, but I have been told this. That water with minerals helps with salivation and some of the minerals are necessary for biological functions. It makes sense, DI water can have a dry after taste because it takes these minerals from your mouth.
The short story to a complicated questions is: Yes, you shouldn't drink it, but no, it won't hurt you. I just wouldn't make a habit of it.
DI Water is great for brewing beer because we can manage our water profile easier. Which is your goal now that you are managing your water profile! We know what is in DI Water - Nothing. So we know exactly the amount of each mineral to add depending on your brew. Giving you flexibility with your water profile for different styles and making the process easier.
DI Water is also good for making tea and coffee. Because water that is pure is such a good solvent - extracting taste, caffeine, etc from tea and coffee become stronger than tap water (Especially very hard water). Places like Starbucks use purified water in their coffee - also to avoid scaling on the equipment - when minerals are left behind on the coffee equipment they can clog water lines.