To limit the probability that individual shower heads will not be equipped with an integral means of limiting the water flow, which could lead to excessive use of hot service water, which could lead to unnecessary consumption of energy for service water heating, which could lead to excessive use of energy, which could lead to an unacceptable effect on the environment.
To exempt from the water flow limits, individual shower heads that are required to have higher flow rates to fulfill their intended use, which relates to safety.