Impact of home industries on water quality in a tributary of the Marimba River, Harare: implications for urban water management

Abstract

Sustainable use of water resources requires the integration of demand management with source quality management. The City of Harare is a case in point, where wastewater and runoff from the city flow into its reservoirs. Little has yet been established on the quality of runoff from home industries in the high-density urban environment. In Harare, most of these are located close to streams draining into the city’s reservoirs. The impact of runoff from different land uses on water quality in a tributary of the Marimba River, Kuwadzana high-density suburb, Harare, was assessed. The water quality from two sub-catchments, one of which contained home industries and residential areas and the other, which contained residential areas only, was compared over the 2001–2002 rainy season. It was found that phosphate (1.08 mg/l), TKN (3.2 mg/l), ammonia (1.14 mg/l), faecal coliforms (1000/100 ml), iron (6.9 mg/l), and lead (0.53 mg/l) were the major water quality pollutants. The SCS-SA model was used to estimate the runoff in different sampling points. Pollution loads for certain parameters were, on average, four times higher in the sub-catchment containing home industries (287 kg total phosphates, 319 kg TKN nitrate, 115 kg ammonia, 744 kg iron and 41 kg lead), than in the sub-catchment containing residential areas only (74kg total phosphates, 50 kg TKN nitrate, 21 kg ammonia, 138 kg iron and 12 kg lead). This is due to the higher runoff volumes from the area containing the home industries, while the pollution concentrations at both representative points where not statistically different. Accordingly, it is recommended that the City authorities should reassess current practice and make provision for sewer and drainage systems and adequate disposal of solid and hazardous wastes in areas zoned for home industries and to improve the solid waste management in high-density areas. Efforts should be made to control the storage of materials and scrap in these areas. Most importantly, the City should reconsider the current practice of zoning home industries close to streams.