[Bobbuilder]

In school, we were taught that with shapes of molecules lone pairs reduce the bond angle by 2.5 degrees. What is confusing me is that water has 2 bonding pairs to start with, therefore wouldn't it reduce a linear shape ie 180 degrees by 5 degrees so that the bond angle for water is 175 degrees? I am a little confused about how bond angles work, so I'll be thankful for any help given!

[mjc123]

Water has four valence electron pairs - two bond pairs and two lone pairs. These are disposed in a tetrahedral arrangement. A regular tetrahedron like CH₄ has bond angles of 109°; reducing this by 5° gives 104°, which is about the bond angle in water.
The point is that the lone pairs reduce the bond angle compared to what it would be if the lone pairs were bond pairs - not compared to what it would be if the lone pairs simply weren't there.