Because Oxygen hogs the electrons it has
a slightly
charge.
Positive
Negative

Oxygen has a greater affinity for electrons than hydrogen, so the oxygen of water "hogs" the electrons and therefore has a slight negative charge (δ-).

Explanation:

Because of in the covalent bond between oxygen and hydrogen, the oxygen atom attracts electrons a bit more strongly than the hydrogen atoms. The unequal sharing of electrons gives the water molecule a slight negative charge near its oxygen atom and a slight positive charge near its hydrogen atoms.