CCWI2017: F101 'END-USE ESTIMATES OF WATER DEMAND WITHIN CERTAIN RESIDENTIAL CATEGORIES IN THE CITY OF JOHANNESBURG'

Increasing drought in many South African communities is driving the need to accurately estimate the end-uses of water within different categories of water users and as a consequence, to realistically determine by how much water use can be reduced. In some water catchments, the accurate estimation of different end-uses is urgently needed given the recent limitations put in place to curtail water. This study, which is part of a larger study commissioned by Johannesburg Water, provides theoretical estimates, using REUM, for end-uses of water for several middle-income homes in a study area served by Johannesburg Water. For indoor end-use, 1, 2, 3 and 4 people per household were modelled and for outdoor end-use, specifically garden irrigation, two cases were modelled i.e. plot sizes of 500m2 (15% irrigated area) and 1500m2 (35% irrigated area). For indoor end-use, parameters that are noted to be quite variable include: shower event volume (shower flow rate and duration); shower- and bath frequency; washing machine event frequency and toilet flush frequency. The results validate earlier reports i.e. that the largest 4 end-uses (i.e. toilet, bath-shower and washing machine) contribute 81.5% to total indoor water use, with the shower being the most notable indoor end-use. Outdoor water use for the 1500m2 plot (35% irrigated area) is notably higher in summer (i.e. December to February), when rainfall is prevalent, than indoor use. This large water requirement is explained by the difference between the evaporation rate and rainfall in the summer months. On the other hand, for the 500m2 plot (15% irrigated area), the garden irrigation requirement is notably less than indoor end-use, irrespective of household size. At this stage of the project, it is apparent that Water Demand Management measures should target the identified notable indoor end-uses (i.e. toilet, shower, bath and washing machine) for relatively smaller properties. For larger properties however, the focus should be on reducing garden irrigation.