Drinking water or wastewaters, in different volumes, contain suspended material, solids that can be settled at rest or dispersed solids that do not settle easily. A substantial part of those solids that do not settle may be colloids. In natural conditions, they cause cloudiness, color, smell, taste and solids. Water purification processes involve the collection of colloidal material, which is indispensable in the purification and treatment processes of wastewater. The coagulation and flocculation operations destabilize the colloids and make them settle. This is usually obtained with the addition of chemical agents and the application of mixing energy. The Flocculation Test Unit “PEF” allows to study the coagulation and flocculation operations and to analyze the main parameters that determine the colloids removal operation.