Sodium Metabisulphite - 1 lb

Campden powder
Used in brewing to remove the chlorine/chrloramines typically found in tap water.  Used in wine and cider making to kill wild yeast or to stop fermentation. Can be used as a preservative in wine.
As a sanitizer - use 2 oz per 1 gallon of water.
As an antioxidant & bactericide - use 1/4 teaspoon to 6 gallons. Dissolve sulphite in warm water before adding