What was in the glass of water that wasn’t in the bottle Hillary Clinton was holding?

While the Democratic presidential candidate was talking to reporters aboard her campaign plane on Monday, she suffered her second massive coughing fit of the day.

Instead of taking a drink from the bottle of water that was in her hand, an aide handed her a glass of water.

Strangely, she didn’t wave off the glass, but instead drank from it, and not from the bottle, which she passed to the staffer.

Why?