Question

If water decreases friction then why we have to aplly a lot of force to move a notebook lying on a wet wodden surface

Answer 1

You have to understand that water does not always act as a lubricant.sometimes it may act as a glue.
When a small amount of water is present between two solid objects, the water forms many isolated disc-like shapes, with a thin ring of surface exposed to air at each water location. This results in a net attractive force between the two objects due to the surface tension of that water-air interface.That is what the case mentioned by u.here the adhesive force between book and bench becomes higher so that u have to apply more force