Use in brewing to remove the chlorine/chloramines typically found in tap water. 
Campden tablets are a common ingredient used in home brewing and winemaking to prevent spoilage and bacterial growth during fermentation. They are made of a combination of sulphites, such as potassium or sodium metabisulphite, and are used to sanitize equipment, prevent oxidation, and kill unwanted yeast and bacteria.
Campden tablets are typically added to the must (unfermented juice or wort) before fermentation to kill any naturally occurring yeast and bacteria that could spoil the final product. They are also added to finished wine to prevent spoilage and bacterial growth during storage and aging