This work reports the design, numerical modeling, and optimization of a new solar water heater using a heat pipe parabolic trough collector (HPPTC) with low concentration ratio. The heat pipe evaporator is positioned on the focal axis of the reflector, while the condenser section is completely immersed in the water cylindrical tank. The copper wire mesh wick is used as the capillary structure, and the working fluid is distillated water. The proposed model operates in transitory regime under the weather conditions of Casablanca city in Morocco. The intensity of direct solar radiation was estimated by the Kasten model assuming a total sun tracking. The finite difference method has been used to solve governing equations. Several optimization types have been investigated and proved that the optimal configuration is obtained by correctly choosing the geometrical and physical parameters of the system. The thermal efficiency for this configuration with a single heat pipe is about 68.45%. This high performance show that the incorporation of a heat pipe as absorber in a PTC may be a better alternative than conventional heating systems.