Investigation of productivity and efficiency of a passive solar desalination technology for brackish water in North-Central Namibia.

Brackish groundwater exists in the ground as part of a major stock of water on earth. This water can be considered as a source of drinking water in Namibia. Attempts have been made in north-central Namibia in recent years to produce safe drinking water from groundwater, using various technologies. These include the plant at Okashana trial which produced drinking water of good quality using solar-powered desalination systems (von Oertzen & Schultz, 2008). In spite of efforts to produce and supply drinking water countrywide, many rural communities in north-central Namibia are less likely to get access to safe drinking water. There are several factors that contribute to the shortage of drinking water; the issue of scarce surface waters, lack of alternative water supply technologies and the challenges related to the distribution of the rural population. Population in northern Namibia is around 922 065 people distributed sparsely in five regions (Namibia Statistics Agency, 2011). Around 8.59% of the northern population live in five towns, while 91.41% is scattered in rural areas. Namibia Water Corporation (Namwater) treats and distributes drinking water countywide including water supply in northern regions. Due to the scattered distribution of rural populations, some communities in remote settlements are not supplied with water by the Namwater distribution network ( Liehr, Papangelou, Brenda, Urban, & Kluge, 2015). As a result, some communities rely heavily on brackish water of poor quality supplied from hand-dug wells and active boreholes with salinity around 2000mg TDS/l and beyond. Water with salt content greater than 2000 mg/L total dissolved solids (TDS) is too salty to drink (National Research Council, 2008). Perhaps, the greatest hindrance of water distribution in Namibia is the issue of limited perennial rivers in the interior. Non-perennial surface water bodies in north-central Namibia occur during rainy seasons in Oshana and drain toward the Etosha Pan where it evaporates completely before summer. Groundwater aquifers in northcentral Namibia are mostly brackish with salinity ranging between that of fresh and seawaters, making it unsuitable for human and livestock consumption. Although research is clear on the suitability of water desalination using solar stills, further studies are needed to explore the potential of small scale desalination technologies for the supply of safe drinking water in remote settlements. A passive solar still is a technology suitable for purification of brackish water in remote settlements. This article describes a study conducted with passive solar stills in order to produce drinking water from brackish groundwater. The aim of the study was to determine the productivity and efficiency of passive solar desalination units (SDU). Samples of brackish groundwater collected from remote settlements were distilled using passive solar stills. The results provided insights regarding the design, productivity and efficiency of passive solar desalination units in regions with high solar radiation. The findings revealed the efficiency, productivity, quantity, quality and capacity of the units to produce safe drinking water. Recommendations are made for the removal of all important contaminants, for post-treatment and mineral enrichment of distillate, and for improvement in the design of the condensing cover of the units.