Sodium Metabisulphite is primarily used as a dechlorination agent to neutralise residual chlorine to prevent damage to RO and NF membranes as well as in environmental discharge waters. 

It reacts with chlorine to form harmless chloride ions, thereby eliminating the potential for chlorine-related issues such as membrane damage, taste, odour, and adverse effects on aquatic life. It is also commonly used to preserve RO membranes when idled for longer periods.