What indicates a low chlorine demand in water treatment?

A low chlorine demand in water treatment is indicated by the presence of low amounts of organic matter in the water. Chlorine demand refers to the amount of chlorine that is required to effectively disinfect water, which can be influenced by various factors, including the presence of contaminants.

When organic matter is minimal, there are fewer substances for chlorine to react with before it can perform its primary function of disinfection. This means that more chlorine can remain in the water as a residual, indicating that the demand for chlorine to fulfill its disinfection duties is low. Hence, the condition of having low organic matter directly correlates with an environment where chlorine can effectively act at higher residual levels.

The other options, while they do relate to water quality, do not specifically indicate low chlorine demand. High residual chlorine levels might suggest a low demand, but this is more a result than a direct indicator. Excessive mineral content and high total hardness do not inherently impact the chlorine demand related to organic material and are therefore not indicators of low chlorine demand.