What type of regeneration system is based on the amount of softened water used?

A demand flow controlled regeneration system operates by monitoring the actual amount of softened water used and regenerating the resin based on that usage. This leads to more efficient salt and water usage, as regeneration occurs only when necessary—that is, when a predetermined volume of water has been treated.

In contrast, a timer controlled system regenerates at set intervals regardless of actual water usage. This can lead to unnecessary regeneration cycles and wasted resources when water isn't being used. Twin alternating systems refer to a setup that utilizes two resin tanks that alternate during operation, which does not specifically measure usage. Finally, a chemical feed pump involves the distribution of chemicals for specific treatment processes rather than a system for regenerating softening resins based on usage.

Hence, the demand flow controlled system is the only option that closely aligns with the concept of adapting regeneration based on actual use, leading to a more precise and efficient approach to water softening.