M.Ing. / A one-year investigation on hot water consumption was conducted in South African developed and developing communities of Johannesburg to determine the personal and household average daily consumption of hot water as well as the average hourly (in summer and in winter) and monthly patterns. The motivation for this research project was to provide to engineers and water heaters manufacturers reliable experimental data on hot water consumption from various categories of dwellings. The existing sources of information in South Africa being extremely limited and results of estimations. The necessary information was collected from hourly and monthly measurements taken by monitoring hot water systems in different dwellings including, houses (300 units), traditional houses (90 units), shacks (200 units), apartments (123 units), townhouses (90 units). For the purpose of this study, the selected (not statistically) dwellings were classified into three categories, which are: high-density dwellings representing the developing communities, medium-density and low-density dwellings which represent the developed communities. The results of measurements show that, in general, people living in developed communities (low-density dwellings) use at least 1.4 times more hot water than those of developing communities (high-density dwellings). The patterns of hot water consumption have been determined for monthly and hourly consumption. The former is divided in four sections: summer weekdays, winter weekdays, summer weekends and winter weekends. The differences between sections are the specific times of peaks and the consumption. The results of this study should be of great assistance to engineers and water heaters designers in analysing existing systems for performance improvement, and in sizing more efficient and suitable systems to South African use.