Which of the following tests is primarily used to measure the effectiveness of purification systems in removing dissolved ions?

Conductivity testing is a key method for assessing the effectiveness of purification systems in removing dissolved ions from water. Conductivity measures how well water can conduct electricity, which is directly related to the concentration of dissolved ions present in the water. When purification systems, such as reverse osmosis or ion exchange systems, effectively reduce the concentration of these ions, the conductivity of the water decreases.

In this context, high conductivity indicates a larger number of dissolved ions, suggesting that the purification system might not be functioning optimally. Conversely, low conductivity readings indicate effective purification and a reduced presence of dissolved ions, confirming the system's capability to purify water. This relationship makes conductivity testing a straightforward and efficient method for evaluating ion removal efficacy in water treatment processes.

Other testing methods mentioned serve different purposes. For instance, the heterotrophic plate count assesses microbial contamination, chlorine level testing gauges the presence of chlorine (which is important for disinfection), and color testing is used to evaluate aesthetic qualities or the presence of certain contaminants but does not specifically measure dissolved ions. Hence, conductivity testing stands out as the most relevant for the intended assessment of purification systems.