The answer to 'what causes water softener' is that a water softener is used to remove minerals, primarily calcium and magnesium, from hard water. Hard water can cause buildup in pipes, appliances, and fixtures, leading to decreased efficiency and lifespan. A water softener uses an ion exchange process to replace the hard minerals with sodium or potassium ions, effectively 'softening' the water.
The main causes of needing a water softener are high mineral content in the water supply, which is common in many areas with well water or municipal water that comes from groundwater sources. The degree of hardness can vary significantly by location, so it's important to have your water tested to determine if a softener is needed.