What are the four types of pressure membrane recognised for the treatment of water?

Water treatment membrane is the process in which it removes all the unwanted substance from the water. Basically, the water treatment process  facilities the different types of the membrane for uses in the process of cleaning the water surface for drinking.  

There are basically four types of pressure driven membrane recognised for the treatment of water are:

qualitative observation deals with data that can be observed with our senses: sight, smell, touch, taste, and hearing. they do not involve measurements or numbers. for instance, colors, shapes, and textures of objects are all qualitative observations.