A supervisory-fluid-adjusted friction-loss coefficient based fire suppression sprinkler system has an array of pipes in fluid communication with an arrangement of sprinklers. A supervisory fluid sub-assembly is fluid communication with the array of pipes. The supervisory fluid sub-assembly provides a supervisory fluid other than air to the array. A diameter of each respective pipe of the array is determined by a friction-loss formula having a friction-loss coefficient representing a metric corresponding to a corrosion-induced internal surface roughness of each respective pipe of the array The friction-loss coefficient is determined by empirical testing of a representative pipe of the array in accordance with a nationally recognized testing procedure.