Assessment of health-related risks associated with domestic water uses in the Mekong Delta of Vietnam

Abstract

The Mekong Delta in the South of Vietnam is characterized by its intensive agricultural production. Access to safe and clean water supplies for drinking and domestic services is poor, especially for rural communities. Water-related diseases are prevalent and may lead to loss of income to families, threat economical development in the region and may even lead to increased morbidity. This study aims at defining health-related risks associated with the use of different drinking/domestic water sources and providing advices to authorities in Vietnam on how to reduce incidences of water-related diseases. The quality of 248 surface-, 116 ground-, 78 household harvested rain- and 41 piped-water samples were assessed for salinity, nutrients, metal(loid)s and microbial indicator bacteria. In addition, 40 household-stored surface- and groundwater and 10 bottled water samples were collected for reference data. Water quality maps were developed to identify hot-spot areas of pollution for surface- and groundwater. Furthermore, 532 household interviews were conducted in the Can Tho, Hau Giang and Soc Trang provinces during November 2011 – September 2012 to assess people’s use as well as perception and handling practices towards these water sources.<br /> All investigated water sources were contaminated at levels that may pose risks to human health. Surface water in lower order canals, which are intensively used by rural communities for drinking and domestic purposes, is heavily polluted by (untreated) waste water, soil leaching and agrichemicals, leading to elevated concentrations of nutrients, metals and pathogens. In coastal areas, sea water intrusion render the surface water saline and hence unsuited for domestic or agricultural uses. Groundwater is particularly contaminated with nutrients and metals, including manganese and arsenic, and occasionally with pathogens. Due to intense over-exploitation of groundwater sources for drinking water supply and irrigation, many groundwater bodies have become saline and unsuitable for drinking. Groundwater must in future be used sparingly to avoid a further decline in its quality. The rainwater harvested by household contains elevated concentrations of pathogens due to unhygienic handling and storage practices. Also lead (Pb) was detected in harvested rainwater originating most probably from gutter systems. The quality of piped-water varied considerably between investigated stations. Especially in remote rural areas, supply stations often provide water of insufficient quality. Consequently, many households prefer resorting to alternative water sources for drinking and domestic uses, leading to poor maintenance and even the abandonment of supply stations. The quality of bottled water requires more detailed investigations as hundreds of brands of bottled water are currently marketed to communities in the Mekong Delta. While poor water quality is widely recognized, most inhabitants of the Mekong Delta are not truly aware of the risks associated with its use and consumption. In general, people perceive water as clean and safe for use when physical conditions like smell, color, taste and odor are positively judged. As a result, perceived clean water sources are generally not treated via i.e. alum and/or disinfected prior to consumption although it may be severely contaminated and pose a risk to human health. Particularly the household harvested rainwater is generally not treated or disinfected and entails the highest health-related risks from all investigated water sources as it is frequently contaminated with E. coli and other coliform bacteria. Despite being generally treated with alum (Al-chloride), surface- and groundwater contain the highest concentrations of metal(loid)s, potentially causing severe health-related risks. Moreover, the alum treatment does not effectively remove arsenic and contaminated surface- and/or groundwater may be unsafe to drink even when people apply treatment. <br /> The development of piped-water supply station is seen, by (inter)national organizations and governments, as the main solution to provide access to safe and clean water. However, the predominant rural populations of the Mekong Delta have limited access to piped-water supply. Therefore, the use of harvested rainwater during the wet season and in some instances of ground- and/or surface water during the dry season may be recommended to rural communities, provided that the users are aware of associated health-risks and are educated in applying appropriate treatment prior to consumption. Such treatments may comprise disinfection of surface and rain water and water filtration by sand and stone filters to reduce metal concentrations in groundwater.