The current paper aims at the establishment and validation of reference cost functions for different types of assets of water supply systems based on known hydraulic (e.g., flow, pump head, pump power) and physical (e.g., volume, material, nominal pressure, diameter) characteristics of the assets. A five-step methodology was followed: (1) database construction and asset characterization; (2) present cost value calculation; (3) key parameters and cost function establishment; (4) model specification; and (5) model testing and validation. A sample of cost and infrastructure data from several Portuguese water utilities has been used. Multiple linear regression analysis has been carried out to obtain cost functions. Cost modeling also includes the estimation of prediction bands to describe cost uncertainty. Developed cost functions have been tested and validated using 10% of randomly selected data