Different materials refract light by different amounts. Refraction occurs because light travels at different speeds in different media. 
The refractive index n = c / v where c = speed of light in a vacuum and v is the speed of light in that particular material. 
If light travels from water to glass it is refracted towards the normal. 
To calculate the angle of refraction:
The refractive index n = c / v where c = speed of light in a vacuum and v is the speed of light in that particular material. The Law of Refraction
The sine of the angle between the normal and the incident ray multiplied by the refractive index is a constant. When light travels from one medium to another:n1 sin θ1 = n2 sin θ2Calculating the Angle of Refraction.
Recall:If light travels from water to glass it is refracted towards the normal. To calculate the angle of refraction: