BeF₂ has zero dipole moment, whereas H₂O has a dipole moment because

The geometry of BeF₂ molecule is linear and the hybridization is sp. In BeF₂ molecule, both the dipoles act in opposite directions by bond angle180° . So, the net dipole moment is zero. Water molecule has a net dipole moment this is because the geometry of water molecule is bent or angular with the bond angle 104.5° .Hence, the dipoles acts in water are not cancelled out like BeF₂ . Let us see the diagrams in the below.