How to measure the water-repellency or “hydrophobicity”
The measurement that defines how water-repellent a surface is after being treated with a hydrophobic coating is called “contact angle”, also called ‘wetting angle’, which is the angle formed by the material’s surface and the tangent of the interface between the fluid (i.e.: water) and the environment at the point of contact (the glass surface for example).
Visit this Wikipedia webpage or further “contact angle” information