I think that you will find that a unit that contains DI will also come with a warning from the manufacturer about using it as drinking water. Here are some excerpts I grabbed from internet discussions regarding consumption. As you can see, there is a difference of opinion. Personally, until such time as there is a definitive study, I would avoid it. You could just take out the DI filter and run that chamber empty.
OPINION #1
When the Langlier Saturation Index reflects a positive value in a water, the water is said to be scale forming. This means that the water contains hard constituents such as Ca and Mg. To a certain extent, this is favorable in commercial water delivered from water treatment plants because of it's tendency to form a scale around the inside of municipal and domestic plumbing thus preventing ******** corrosion of water piping. When the LSI has a negative value the water then becomes aggressive. The lower the value (down to -5) the more aggressive the water. Aggressive water causes corrosion to all metals.
Water is considered the universal solvent. In it's purest form having a neutral pH, the water has the most solubility. I don't believe deionized water is safe to drink because of its "leaching" ability's. Deionized water will strip CO2 from the air. When you drink it, this water will strip vitamins and minerals from inside you. Drinking small amounts of deionized water from time to time may be all right however, long term effects from consistent consumption may have adverse results on health.
OPINION #2
Deionized water is harmless. Drink all you want. The water will quickly dissolve some sugars and electrolytes from your mouth and especially from your digestive system, and will become just plain water. The only potential harm from deionized water might come from the resin used to demineralize the water--not only are these resin beds somewhat limited in their capacity, but they are also hospitable breeding grounds for bacteria. In general, however, the bacteria which grows in clean water is usually harmless. The problem with deionized water is the cost--it is just not worth the price from a drinking water perspective when so many other, less expensive, water purification systems exist.
By the same token, mineral water, with a total dissolved solids of more than 1000 parts per million, is also no better or worse for you. From a nutritional standpoint, there are almost no nutrients or minerals in any potable water, certainly not enough to be nutritionally significant, including expensive designer waters.
Distilled water and deionized water do not taste very good straight from the treatment source. To make these pure waters more palatable, chill them and shake them before serving to aerate a bit. Store bought distilled water is usually shipped in high density polyethylene bottles which are permeable to oxygen, so this distilled water is pre-aerated. Regular bottled water from a reputable company and filtered tap water are still the best source for pleasant tasting water. Don't believe the hype; from a health perspective, distilled, deionized, drinking, demineralized, spring, mineral, fluoridated, tap, etc., are all about the same from a nutritional and health perspective. Taste is an issue, but carbon filtering will take care of the bulk of that item, and biologic safety is addressed by sanitation. As far as other contaminant issues in the western world, the water supply system is completely safe in almost all cases, and for the worriers, filtration and commercial bottled water can fill in the rest.
OPINION #3
Deionized water is an usually pure form of water. Water actually is a very aggressive solvent. In our normal contact with water, it already has a lot of things dissolved in it, and is pretty tame. Deionized water is so aggressive that it will begin to attack metal, plastic, or even stainless steel. It will dissolve carbon dioxide in the air. If someone was to drink deionized water, it would have the opposite effect of a vitamin, drawing out the minerals and vitamins in your body. It is common knowledge that drinking deionized water is harmful, but I am not sure if there are any documented studies.
More opinions can be found by googling "drinking de-ionized water"