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As in many other cities, urbanization coupled with population growth worsens the water supply problem of Addis Ababa, Ethiopia, with a water supply deficit of 41% in 2016. To investigate the potential contribution of rooftop rainwater harvesting (RWH) from large public institutions, 320 such institutions were selected and grouped into 11 categories, from which 25-30% representative 588 rooftops were digitalized and the potential RWH volume computed based on a ten-year rainfall dataset. When comparing the resulting RWH potential with the water consumption, up to 2.3% of the annual, potable water supply can be provided. If reused only within one's own institution, the self-sufficiency varies from 0.9 to 649%. Non-uniform rainfall patterns add uncertainty to these numbers, since the size of the storage tank becomes critical for coverage in the dry season from October to May. Despite the low replacement potential at the city level, RWH from large institutions will enable a significant volume of potable water to be transferred to localities critically suffering from water shortage. Further, large institutions may demonstrate how RWH can be practiced, thus acting as a frontrunner for the dissemination of RWH to other types of rooftops. To narrow the water supply gap, considering rooftop RWH as an alternative water supply source is recommended. However, the present study assumed that financial constraints to install large sized storage tanks are considered as a possible challenge. Thus, future research is needed to investigate the cost-benefit balance along with the invention of a cheap storage tank as they may affect the potential contribution of RWH from rooftops., Competing Interests: The authors declare no conflict of interest.

In rapidly urbanizing catchments, increase in stormwater runoff may cause serious erosion and frequent floods if stormwater management systems are improper and dysfunctional. Through GIS-based modelling, field investigations, resident’s questionnaire survey, and interviews with officials, the study set out to assesses the coverage and efficiency of drainage infrastructure in Mbezi River catchment basin in Dar es Salaam, Tanzania. Between 2003 and 2016, the catchment imperviousness increased by 41%, causing flood incidents, massive erosion, and numerous pollution sources. Residents strive to address stormwater hazards using terraces, hedges, and physical barriers; however, the problems persist, indicating lack of coordination and poor causality understanding between land-use changes and catchment impacts. Small-scale stormwater harvesting was exercised by 75% of the households, pointing to water supply challenges. Municipal stormwater management efforts was limited to roadside drains covering 17% of road lengths in the catchment, and 65% of those did not meet their design standards. Interviews with officials revealed a need for improved co-understanding and collaborative initiatives to bolster integrated water management. The study suggests a need to adopt a new urban stormwater management paradigm, appropriate for both residents and authorities. Without this new discourse, the urbanization led stormwater increase might jeopardize the liveability of the entire catchment.

The article offers information on examining and comparing efficiency of stormwater treatment facilities (STFs) by using parameters of a minimum data set of water quality. It is said that urban stormwater impacts aquatic ecosystems and restricts the use of stormwater runoff for recreational purposes. The efficiencies of STFs are not well documented due to the highly variable runoff hydrograph. The use of the minimum data set will ensure broad spectrum testing at low costs and strengthen comparability among STFs.