I can't say how detrimental drinking DI water would be, but I have worked with it in a couple of laboritories. Drinking DI is always on the safty list of things NOT to do. Your body uses ions to do alot of things: Absorb food and water, maintain nervous and muscular function, and your kidneys use ions to aid in getting rid of waste. DI water would be dificult for your body to absorb and when and if it did it would unbalance the levels of ions in your body. If you want to know more get a biology book and look up kidney function, hypotonic, and hypertonic solutions. If you manace to absorb a large ammount of DI water it can cause your blood cells to get bloated or even burst.
Drinking DI water is like putting a salt water fish in fresh water. It will stress your system.