In the short term, drinking deionized water isn't going to cause any immediate health effects for the vast majority of people. There is some small risk that there could be a residual traces of the deionizing resins still in the water, but this is unlikely.

Why deionized water is bad for you?

The Risks of Deionized Water

Due to the fact that deionized water is lacking in ions, it can absorb the ions in your body upon drinking it. Because magnesium and calcium are both easy for deionized water to absorb, it can also steal these tissues.

Is deionised water hazardous?

4.2. Most important symptoms and effects, both acute and delayed Inhalation May cause irritation. Ingestion May cause irritation.