The International Development Research Centre is a public corporation created by the Parliament of Canada in 1970 to support research designed to adapt science and technology to the needs of developing countries. The Centre's activity is concentrated in six sectors: agriculture, food, and nutrition sciences; health sciences; information sciences; social sciences; earth and engineering sciences; and commwtications. IDRC is financed solely by the Parliament of Canada; its policies, however, arc set by an international Board of Governors. The Centre's headquarters arc located in Africa, Asia, Latin America, and the Middle East. IDRC-TS65e Solar-Powered Desalination A case study from Botswana by R. Yates, T. Woto, and J.T. Tlhage © International Development Research Centre 1990 PO Box 8500, Ottawa, ON, Canada KlG 3H9 Yates, R. Woto, T. Tlhage, J.T. IDRC-TS65e Solar-powered desalination : a case study from Botswana. Ottawa, Ont., IDRC, 1990, viii + 55 p. : ill. (fechnical study I IDRC) /Desalination/, /drinking water/, /water supply/, /solar energy/, /Botswana/ - /appropriate technology/, /costs/, /maintenance and repair/, references. UDC: 551.464:628.16(681) ISBN: 0-88936-554-7 A microfiche edition is available. The views expressed in this publication are those of the authors and do not necessarily represent the views of the International Development Research Centre. Mention of proprietary names does not constitute erulorsement of the product and is given onl,y for information. Printed in Singapore Abstract In Africa, chronic drought conditions are reducing access to and the quality of drinking water. In Botswana, recurring droughts have left 80% of the population reliant on water from boreholes. Drilling such boreholes is an expensive proposition and the water is often scarce or saline. One possible solution to this dilemma is solar desalination. The Solar Energy Section of the Rural Industries Innovation Centre (RIIC) in Kanye, Botswana, has been studying solar distillation methods since 1977. This book summarizes the results of an intensive 3-year field study carried out by RIIC, with the support of IDRC (International Development Research Centre), on the technical performance and suitability of various small-scale desalinators. Their findings indicate that small-scale desalinators can provide a clear, palatable distillate; that certain models can provide a constant and adequate supply of potable water when the distillate is added to salty water from traditional sources; and that the technology is readily acceptable to remote area dwellers (RADs). The study also highlights the importance of including intended beneficiaries in the management of a new technology, in this case, the siting, construction, operation, and maintenance of the desalinators. Resume En Afrique, la secheresse chronique reduit la quantite et la qualite de l'eau potable. Au Botswana, Jes secheresses repetees ant contraint 80 % de la population a compter sur Jes forages pour leur eau. Couteux a realiser, ces forages souvent sont presque secs ou contiennent une eau salee. Le dessalement solaire offre peut-etre une solution a ce dilemme. La Section de l'energie solaire au Rural Industries Innovation Centre (RIIC, Centre d'innovations industrielles rurales) a Kanye, Botswana, etudie Jes methodes de distillation solaire de I' eau depuis 1977. Dans cet ouvrage sont resumes Jes trois annees de travaux intensifs realises par le RIIC avec I' aide financiere du CRDI (Centre de recherches pour le developpement international) sur le rendement technique et la pertinence de divers petits alarnbics. La conclusion des travaux est que ces appareils peuvent foumir un distillat limpide et agreable au gout; que certains modeles produisent une quantile d'eau potable constante et suffisante lorsque le distillat est ajoute a l'eau salee puisee aux sources habituelles et que la technologie serait bien accueillie par Jes habitants des regions reculees. L' etude souligne aussi !'importance d'inclure Jes beneficiaires vises dans la gestion d'une nouvelle technologie, dans ce cas-ci le-choix de !'emplacement, l'amenagement, !'exploitation et la maintenance des installations de dessalement. Resumen En Africa, la sequfa cr6nica esti reduciendo las suministros de agua y su calidad. En Botswana, sequias recurrentes han hecho que el 80% de la poblaci6n dependa de! agua de pozos, la perforaci6n de las cuales es muy costosa y el agua de las mismos escasa y salina. Una posible soluci6n a este dilema es la desalinizaci6n solar. La Secci6n de Energia Solar de! Rural Industries Innovation Centre (RIIC, Centro de Innovaci6n de Industrias Rurales) en Kanye, Botswana, ha estado estudiando las metodos de destilaci6n solar desde 1977. Este libro resume las resultados de un estudio de terreno iii intensivo de 3 a:i'ios, llevado a cabo por el RIIC con apoyo del Centro Internacional de Investigaciones para el Desarrollo (CITO). El estudio se centr6 en el rendirniento tecnico y lo apropiado de varios desalinizadores de pequeiia escala. Los resultados del estudio indican que los desalinizadores de pequeiio calibre pueden destilar un agua clara y aceptable; que ciertos modelos pueden proporcionar un suministro adecuado y constante de agua potable cuando el destilado se a:i'iade al agua salada proveniente de fuentes tradicionales; y que la tecnologfa ya se acepta por pobladores de areas remotas (PAR). El estudio subraya tambien la importancia de incluir a los beneficiarios objeto del proyecto en la gesti6n de una nueva tecnologfa, en este caso el asentamiento, construcci6n, operaci6n y mantenirniento de los desalinizadores. iv Contents Foreword . vii 1. Introduction . 1 The Kalahari remote area dwellers . 3 Fundamentals of RADP . 6 2. Choosing a technology . 7 Reticulation . 8 Trucking . 8 Desalination . 9 3. Designing stills for harsh conditions ............... 14 Mexican stills ............................ 14 Brick stills . 19 4. Installing and operating the stills ................. 24 Installation . 25 Monitoring and operating . 33 S. Maintaining the stills . 37 Cleaning the basin . 37 Cleaning the glass . 37 Cleaning the hatches . 39 Inspection and repairs . 39 6. Comparing costs of alternative technologies . 43 7. Conclusions ............................... 47 Afterword . 49 Findings of the postproject evaluation . 49 Conclusions . 53 References . 55 v Foreword Chronic drought conditions in Africa are reducing access to, and quality of, drinking water, particularly for those living in arid regions. Surface water sources and shallow wells are not being replenished naturally. Drilling boreholes to access deep, subterranean water tables is expensive and requires sophisticated drilling and pumping equipment. Transporting water supplies to remote communities is difficult and expensive. Consequently, per capita water consumption is severely restricted. Also, water from shallow, hand-dug wells, abandoned boreholes, and surface water sources is often brackish and salty. The lack of sufficient and potable water can only adversely affect the health of arid region dwellers. Since 1977, the Solar Energy Section of the Rural Industries Innovation Centre (RIIC), a nongovernmental organization (NGO) located in Kanye, Botswana, has been carrying out research on solar distillation methods. The objective of their program is to improve the quality and increase the quantity of drinking water for people living in remote areas, particularly for the remote area dwellers (RADs) in the Kalahari Desert. The findings of RIIC's initial studies indicated that desalinators provide a clear and palatable distillate. In 1983, RIIC approached IDRC (International Development Research Centre) for financial support to carry out an intensive, 3-year field study on the technical performance of small-scale desalinators and their suitability to the RADs. The results of the project confirmed that • if properly constructed and maintained, certain desalinator models provide a constant and adequate supply of potable water when the distillate is added to salty water from traditional sources, and the technology is readily acceptable to the RADs. The project also highlighted the need to account for managerial aspects related to the promotion and maintenance of the technology, particularly the active participation of the intended beneficiaries in siting, vii constructing, operating, and maintaining the desalinator units. If the intended beneficiaries are not involved, the technology will not be used correctly, or perhaps not used at all; community members will continue to perceive the technology as a gift from, and therefore a responsibility of, the government. IDRC believes that the findings of this project provide useful insight into the use of small-scale desalination methods, particularly for government agencies and NGOs involved in planning and promoting the use of such devices. The publication of this report is intended to increase knowledge in these areas, so as to improve the planning and execution of similar projects designed to increase accessibility to drinking water for communities located in arid regions of the developing world. James B. Chauvin Senior Program Officer Health Sciences Division International Development Research Centre viii 1 Introduction Obtaining water is one of the major occupations of rural peoples in Africa. In the desert areas, especially during the last 6 years of drought, it has become, for many, a preoccupation. In Botswana, for example, water is scarce and costly at the best of times. Annual rainfall averages