What type of water is characterized by low calcium and magnesium concentrations?

The correct answer, soft water, is characterized by low concentrations of calcium and magnesium, which are the primary minerals that contribute to water hardness. Soft water is typically found in regions where rainfall dissolves fewer minerals from soil and rock, resulting in a lower mineral content. This type of water is often preferred for various applications, such as in aquariums or specific aquatic ecosystems, because it supports certain species of fish and aquatic life that thrive in low-hardness conditions.

Freshwater, while it can also be soft, encompasses a broader category that includes both hard and soft types of water, depending on the specific mineral content. Saltwater, typically found in oceans and seas, has high concentrations of salt and is not classified based on calcium and magnesium levels. Brackish water, which is a mix of freshwater and saltwater, also does not fit the definition of having low calcium and magnesium, as its mineral content varies significantly based on its source.