Which type of water is chemically treated or similar to rainwater?

Soft water is chemically treated to have a lower concentration of minerals, particularly calcium and magnesium, which are the primary components that make water "hard." This treatment process often mimics the characteristics of rainwater, which is naturally soft because it contains fewer dissolved minerals. Rainwater is a result of condensation from the atmosphere, leading to relatively low mineral content.

In contrast, hard water contains higher levels of calcium and magnesium, which can lead to scale buildup and issues with soap lathering. Tap water often contains a mix of minerals depending on its source and may not be treated to remove hardness. Filtered water can vary widely depending on the filtration process used. Therefore, the distinction of soft water as being similar to rainwater and chemically treated makes it the correct choice in this context.