What happens when sequestering agents are used in hard water treatment?

When sequestering agents are used in hard water treatment, they function primarily by preventing metal ions, such as calcium and magnesium, from reacting in a way that causes hardness problems. These agents bind to the metal ions in the water, effectively "hiding" them and keeping them in solution, which reduces their ability to form scale and precipitate out. By doing so, sequestering agents help in controlling the adverse effects of hardness, such as buildup in pipes and appliances, without actually removing the calcium and magnesium ions from the water.

This mechanism allows for easier handling and better performance of water in various applications, such as in heating systems and detergent effectiveness. The other options do not accurately describe the role of sequestering agents: they do not enhance the hardness of water nor do they filter out impurities in the traditional sense. Instead, their primary purpose is to inhibit the reactivity of the metal ions causing hardness.