The oxygen end of the molecule has a partial negative charge and the hydrogen end has a partial positive charge. This is because of the electronegativities of the atoms O and H. O is more electronegative than H so electrons are more often around the O atom. Electrons are negatively charged, so this causes the partial negative charge on the O atom, similarly, the "deficiency" of electrons around the H atoms cause partial positive charges because the nuclear charge (protons) isn't balanced to the number of electrons around it.
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