In water, the central atom, oxygen has two bond pairs and two lone pairs. Thus, it should have a bent shape (please comment if you have any doubts regarding this). The bond angle should be 109.5 degrees, but the bond angle decreases due to repulsion between lone pairs and bond pair-lone pair repulsion.

Note - To understand this answer, you should be clear in the basics of VSEPR theory. If you have any doubts, ask in the comments.
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is repultion b/w bond pair-lonepair is higher than lonepair-lone pair & bondpair-bondpair?
Repulsion between lone pair and lone pair > Repulsion between lone pair and bond pair > Repulsion between bod pair and bond pair
repulsion b/w bond pair-lone pair is NOT higher than lone pair-lone pair. It is higher than bond pair-bond pair repulsion.
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