Quality of Groundwater from Open-Wells in Rural and Peri-Urban Areas of Unguja Island, Zanzibar, Tanzania

Abstract

Water quality is one among the most important environmental issues these decades. Heavy metals receive a particular concern among the wide diversity of chemicals causing environmental degradation including groundwater. Nitrate, as well, is an indicator of human-induced groundwater contamination. This study investigated the levels of toxic heavy metals such as Cd, Cu, Pb, Co and Cr, and nitrate (NO3 –) contained in the water from 116 openwells in rural and peri-urban areas of Unguja Island, Zanzibar. The average values of the heavy metals were as follows: 1.359 ± 3.419 μg L–1 for Cr; 0.052 ± 0.109 μg L–1 for Co; 0.238 ± 0.533 μg L–1 for Cu, 0.001 ± 0.004 μg L–1 for Cd; and 0.003 ± 0.026 μg L–1 for Pb. Referring to Water quality standard in Japan (MHLW), Water quality guideline by WHO and Quality of Drinking Water Supplies (EWURA), the results suggest no serious acute problem of heavy metal contamination so far. The average value of the nitrate (NO3 –) was 36.1 ± 58.85 mg L–1. The nitrate contamination, some of which exceeded the values of permissible standards for safe drinking waters by MHLW and WHO, however, should not be underestimated.