Since the 1940s, the models used to estimate peak water demand has been based largely upon variations and refinements of the probabilistic ‘fixture unit’ model. An approach originally advanced by Hunter (1940) in the United States of America (USA). Seeking an improved approach to the 'fixture unit' model, now widely recognised as outdated, is the key driving force behind the current work. Boosted by the development of computing power, the plumbing industry, researchers, and academics have, over the last decade, developed computational models as a means of estimating peak water demand. This paper builds on computational models embracing the estimation of peak water demand. A brief outline of the fixture unit and its limitations is provided with key developments in computational modeling comprising current developments from the USA and UK. A brief outline of computational models is presented: Modified Wistort Method (MWM); the Exhaustive Enumeration Method (EEM), and the Water Demand Calculator (WDC). Also presented, from the UK, is the Loading Unit Normalisation Assessment method (LUNA) aimed at an improved model to size domestic hot and cold-water systems. The analysis of the computational models suggests the WDC model is conceivably the most compatible with that of the plumbing industry's design requirements. Suggesting this model could easily be adapted to meet the requirements across international borders. Challenges for the international acceptance of the WDC are the field study requirements to determine p (probability of use) and q (fixture flow rate) values for all types of buildings. Keywords: Fixture unit, Peak water demand, Modified wistort method, Exhaustive enumeration method, Water demand calculator, Loading unit normalisation method