What does combined residual indicate in the chlorination process?

Combined residual in the chlorination process refers to the amount of chlorine that has reacted with ammonia and other organic nitrogenous compounds to form chloramines and also includes chlorine that has reacted with other oxidizable materials in the water. This indicates that chlorine has not only been used for disinfection but has also formed stable compounds through its interaction with these substances.

The presence of chloramines is particularly important to note as they can provide a longer-lasting residual effect in the water distribution system compared to free chlorine. This is vital for maintaining water quality as the treated water moves through the distribution network. Thus, combined residual is essential for understanding how effectively chlorine has been utilized and how it continues to protect the water after the initial chlorination process.