Does filtered water remain hard?

Filtering hard water does change the structure of the water - the water remains hard. Water filters and water softeners perform different types of treatments. Use a water filter if you want hard water to remain hard. If you want to soften hard water, use a water softener.

High levels of calcium and magnesium are the two main culprits for hard water. Your best option for filtering hard water is a water softener, which focuses on only removing these hard minerals. Other filters like reverse osmosis technically soften the water, but they also remove all other essential minerals in the process. Carbon filters won't remove any of the minerals.