A sudden change in the pipeline's velocity results in a transient flow known as a "water hammer" in pipes. This phenomenon can cause negative and positive pressure in the pipeline and is often dangerous where the pipe can burst if the pressure is high enough. Therefore, it is necessary to study the variables affecting the water hammer to have a clear understanding of the controlling conditions of the water hammer, which could save the system from failures. This paper investigates the effects of pipe material and diameter on water hammer pressure. Three different pipe materials were examined (Steel, Concrete, and Polyvinyl chloride (PVC)) with different inner diameters (250, 350, and 500 mm). Numerical modeling and analysis are conducted to obtain the minimum and maximum pressure envelopes across the system of pipes. The numerical results obtained from the transient solver show that the normalized piezometric pressure calculated in different statuses directly changes with the change of the pipe material and diameter. The water hammer pressure has reduced significantly in pipe materials with less elastic modulus and larger diameter for the same operating condition.