Is demineralised or distilled water useful for drinking purposes? If not,how can it be made useful?

(N/A) No,demineralised or distilled water is not useful for drinking purposes because it lacks essential minerals like $Ca^{2+}$ and $Mg^{2+}$ ions,which are necessary for the human body.
It can be made useful by adding essential minerals in controlled amounts or by mixing it with a small amount of mineral-rich water to restore the required mineral balance.