A group norm is a code of conduct and standard established by group members applied in a specific environment. It can be divided into two types: descriptive norms and prescriptive norms. Descriptive norms indicate what people should do in a specific situation. It simply tells people which behaviors are effective and suitable. Prescriptive norms specify what people must do in a specific situation, and what behaviors are approved or opposed by people.
Water conservation slogan is according to the above definition, a descriptive norm.