Building Water Supply System is a fundamental unit in Water Supply Systems as it is directly associated with end users. However, the studies available on its efficient design are limited. Water demand estimation continues to be an important issue in Water Supply Systems' design because of its multifaceted nature. Hunter's curve or Fixture Unit method is widely used for estimating the load on Plumbing. Regardless of its popularity, it has few drawbacks and is arbitrarily modified in some Plumbing Codes. Fixture-use probability, a basic entity in the Fixture Unit and some other methods, is a difficult parameter to estimate. Commonly, high-resolution field data is used for Stochastic modelling of Residential water demand which may not be available always. The paper reviews important Residential water demand models in a view of their applicability in Building Water Supply System design. The irregular nature of water demand in buildings is due to uncertainty in water-use behaviour of users at Fixture level. Use of soft-computing techniques can provide an advantage over the other methods in modelling such behaviour. The paper also discusses Reliability of Building Water Supply Systems and applicability of some common indices for estimating Reliability of Building Water Supply System.

Stochastic models for estimating residential water demand use high-resolution field data consuming large costs and significant time. An attempt for the accurate estimation of water demand may result in its complex analytical model due to numerous factors affecting the water use event. Moreover, as the water supply system is always subjected to variations in demand, the accuracy of water demand estimation in its design can be side-lined. The water demand in residential buildings is mainly governed by the users’ characteristics and their daily schedule. In this view, the use of Fuzzy Logic can be advantageous to model the uncertainty in water demands. The presented study attempts to provide a methodology to estimate urban indoor residential water demand with the help of user-based end-use models in the absence of field data and generate various possible water demand patterns of fixtures. Usergroups were created for assuming spatial variations in water demand. Fuzzy Logic was used to develop the end-use models using data on urban users’ characteristics, their diurnal activities, and water use habits to estimate the demand characteristics of fixtures. The model may also facilitate the computation of pipe sizing in building water supply systems.

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