Here's why:

* Electronegativity: Oxygen is more electronegative than hydrogen. This means oxygen has a stronger pull on shared electrons in a covalent bond.

* Electron Distribution: The shared electrons in the O-H bonds spend more time closer to the oxygen atom. This creates a partial negative charge (δ-) on the oxygen and a partial positive charge (δ+) on the hydrogen atoms.

Therefore, oxygen is electron-poor (has a partial positive charge) and hydrogen is electron-rich (has a partial negative charge).