Water end-use estimation can support the urban water crisis management: A critical review

The present study reviews the overall perspectives of end-use studies on urban water crisis management by analysing their beneficial application in water conservation and wastewater recycling. The paper incorporates a critical review of water end-use consumption of 16 major countries from 3 major continents, i.e. Asia, Europe, and Australia. The study reflected a different trend between the water consumption of developed and developing nations, thereby implying a need for separate prospects of end-use results in these countries. Besides, the percentage of greywater generated varies from 54% to 86% of the total indoor household water consumption and thus can be a valuable water resource to solve the urban water crisis. There exists a strong correlation between the amount of greywater generated and the amount of water used for the shower (R² = 0.69) and laundry (R² = 0.50). The same, i.e. R² values, for end-uses of the toilet flushing, dishwashing, and indoor taps with the amount of greywater, were found to be 0.30, 0.26, and 0.04, respectively. Further, except for the end-use pertaining to indoor taps, water consumption of all other end-uses has witnessed an upward spiral in developing countries with time, which may be attributed to the improved accuracy of collected end-use data or increased contribution of 'leaks/others' category. In developed nations like the USA, there is not a single end-use that has shown an absolute increase with time owing to a variety of measures such as increased awareness, education, retrofitting of appliances and several other factors like governmental restrictions. Change in attitude or/and behaviour of people towards water use driven by drought-like experience could also be a valid reason. After this extensive review of the end-use pattern, we proposed specific greywater recycling models that are expected to help engineers, governments, and policymakers in sustainable urban water management.