The soap reacts with the calcium chloride to form soap scum and is not available to suds. Explain why the suds did not form as quickly in the second test tube and in the third test tube. The minerals in the water restricted the formation of soapy water. The reaction of soap with the material dissolved in the water. If the water at your house is hard, how would that affect cleaning your clothes.
Hard water restricts the cleaning function of soap.
The taste of distilled water is flat. The minerals will corrode the pipes, joints, and other parts. This has an affect of making the pipes smaller. Hardness of water may be reduced by filters and softeners. Encourage the students to research what water softeners are and how the water softeners function.