A soft water system is a system that converts tap water (i.e., hard water) into soft water. A complete soft water system typically includes a soft water unit and a pre-filter.

The soft water machine operates by utilizing internal reactions to remove calcium and magnesium ions from the water; the pre-filter is used to filter out impurities in the water to prevent cumulative damage to the soft water machine's internal components.

The core component of a soft water system is the water softener. The most common on the market and the most frequently used at home is the ion exchange water softener, which utilizes the internal resin to exchange calcium and magnesium ions in the water, transforming tap water into soft water. Resins have a lifespan and need to be recharged with special salt after a certain period to reset the resin and restore its effectiveness.