How is water that requires a significant amount of soap for lather described?

Water that requires a significant amount of soap to produce lather is described as hard water. Hard water contains high concentrations of dissolved minerals, primarily calcium and magnesium ions. When soap is added to hard water, these minerals react with the soap to form insoluble compounds, which do not create lather effectively. As a result, more soap is needed to achieve the same suds that would be easily produced in soft water, which has low concentrations of these minerals and allows for a better lather.

Understanding this characteristic of water is essential for water treatment operators, as hard water can impact not just domestic tasks like washing but also equipment and plumbing systems, leading to scaling and decreased efficiency.