The filtration technologies being applied in industries and at home are built around water purification membranes. The membranes are barrier-like and only clean water molecules can go through them, as contaminants like bacteria, viruses, and dissolved salts can be prevented. Their application in water treatment plants on an industrial scale and their application at home through water filters has transformed the way clean water is available. These membranes are of different forms, namely reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF) and microfiltration (MF). The decision is made based on the intended purification requirement, be it desalination or softening of hard water, or pathogen removal.