The primary purpose of municipal water systems is to prevent waterborne illness. Most substances that control the safety of the water supply, however, destroy coffee’s flavor and aroma. Chlorine and chloramines (a compound formed by chlorine and ammonia) are oxidizing aromatics and oils. Because chlorination is standard in all municipal water supplies, removing these substances is necessary for the finest brewed coffee flavor.
Free chlorine refers to chlorine available in the ionic form that oxidizes most easily and is most volatile. Total chlorine includes free chlorine and other chlorine-based substances, some of which are added to maintain chlorine levels throughout the water delivery system. Both free and total chlorine have a deleterious effect on coffee flavor, however, it is free chlorine that has the most reaction in coffee brewing.
