You really wanna mess with people, you can tell them that when DHMO is dissolved in water, it dissociates into hydronium and hydroxide ions. An imbalance of either one can alter the pH of water and make it corrosive and even toxic.
For the chemistry of it, some portion of water molecules form the hydronium ion (H3O+) and others form the hydroxide ion (OH-). It's argued that most bulk water is actually in this form, hydronium and hydroxide ions... Pure water exhibits a pH of 7 because of this phenomena, an equal balance between an acid (H30+) and a base (OH-).