system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between hard and soft water? And why does soap not wash off as well depending on the type?
gpt
So, basically, "hard" water means that there are dissolved bicarbonate minerals present in the water. This usually happens when the water in question filtered through limestone or chalk, which contain calcium and magnesium, though it can also occur with sulfur compounds.

These ions prevent the formation of lather because they destroy the soap's ability to lower the "surface tension" (known as the soap's "surfactance") between the liquid water and whatever you're trying to clean off. This is what gives soap its ability to remove dirt and grime.

While drinking hard water might carry some health benefits due to the mineral content, that same content is very bad from an industrial standpoint because of its tendency to form deposits, known as "scale," inside pipes and heat exchangers. Therefore, the practice of "water softening," removing these dissolved minerals, is very important.