Design shall be such as to ensure reliability of individual pieces of equipment and to avoid interruption to water service. Reliability consideration shall also be taken into account in the location of the pumping station, power supply and choice of equipment. Pumping units and auxiliary equipment should be of ample capacity and in sufficient numbers of units to permit continuance of service with the largest unit out of service. The reliability of individual pieces of equipment depends on their design, construction, installation, ease of maintenance, availability of spare parts, etc. Attention to these factors to avoid interruption of service to customers is justified. (28-ME-DG-02 § 3)