What does free residual chlorine indicate?

Free residual chlorine refers to the amount of chlorine that remains in the water after it has reacted with any contaminants or other substances that may consume chlorine, such as organic matter or pathogens. This measurement is crucial for understanding the effectiveness of chlorine as a disinfectant.

When chlorine is added to water, it begins to react with materials in that water. Some of this chlorine will combine with these materials and become chloramines or other forms that do not contribute to disinfection. The chlorine that remains available to neutralize pathogens and keep the water safe for consumption is what we refer to as "free residual chlorine."

Thus, having a measure of free residual chlorine ensures that adequate disinfection is taking place; it confirms that enough chlorine is still functional and capable of maintaining water quality and safety. If free residual chlorine is present, it signifies that the chlorine demand has been satisfied, which is essential for ensuring the water is free from harmful microorganisms.