What type of water contains salts that prevent shampoo from lathering?

The correct answer is hard water because it contains a high concentration of minerals, particularly calcium and magnesium ions. These minerals can bind to the ingredients in shampoo, making it difficult for the product to lather effectively. When shampoo is applied in hard water, the minerals interact with surfactants (the cleaning agents in shampoo), reducing their ability to create bubbles and foam, which are crucial for effective cleansing.

In contrast, soft water has a low concentration of these minerals, allowing shampoo to lather easily. Distilled water is purified and devoid of minerals, so it also allows for good lathering properties but is not the type of water that specifically affects shampoo usage in the same way hard water does. Mineral water, while it contains various minerals, is not typically associated with significant effects on shampoo lathering when compared to hard water.