Our recent discovery of hazardous concentrations of arsenic in shallow sedimentary aquifers in Cambodia raises the spectre of future deleterious health impacts on a population that, particularly in non-urban areas, extensively use untreated groundwater as a source of drinking water and, in some instances, as irrigation water. We present here small-scale hazard maps for arsenic in shallow Cambodian groundwaters based on >1000 groundwater samples analysed in the Manchester Analytical Geochemistry Unit and elsewhere. Key indicators for hazardous concentrations of arsenic in Cambodian groundwaters include: (1) well depths greater than 16 m; (2) Holocene host sediments; and (3) proximity to major modern channels of the Mekong (and its distributary the Bassac). However, high-arsenic well waters are also commonly found in wells not exhibiting these key characteristics, notably in some shallower Holocene wells, and in wells drilled into older Quaternary and Neogene sediments.It is emphasized that the maps and tables presented are most useful for identifying current regional trends in groundwater arsenic hazard and that their use for predicting arsenic concentrations in individual wells, for example for the purposes of well switching, is not recommended, particularly because of the lack of sufficient data (especially at depths >80 m) and because, as in Bangladesh and West Bengal, there is considerable heterogeneity of groundwater arsenic concentrations on a scale of metres to hundreds of metres. We have insufficient data at this time to determine unequivocally whether or not arsenic concentrations are increasing in shallow Cambodian groundwaters as a result of groundwater-abstraction activities.

Most water supply programmes in Cambodia have focused on providing access to bacteriologically safe water, an approach which has led to an increasing reliance on ground water, especially in rural areas. However, there have been very few data collected on the chemical quality of the nation's drinking water sources, and few water supply programmes have the capacity to assess chemical quality. The study was designed to address this data gap by conducting a low-cost, rapid assessment of drinking water sources nationwide to determine whether there were any chemicals of concern in Cambodian water supply sources. Results of the assessment confirm that there are several parameters of health and aesthetic concern; dissolved arsenic is the most significant. Elevated arsenic levels (some exceeding 500 microgl(-1)) were detected in aquifers of moderate depth in several highly populated areas, confirming that further investigation of the occurrence of arsenic contamination in Cambodia is warranted. Other chemicals of health concern include nitrate, nitrite, fluoride and manganese. Additionally, many ground water sources are negatively impacted by parameters of aesthetic concern, such as iron, manganese, hardness and total dissolved solids. Elevated levels of these parameters have caused consumers to reject newly installed water supplies, often in favour of surface water sources that are bacteriologically unsafe.

Across Southeast Asia many of the poorest communities live on marginal land or over water. Owing to adverse geographic and climatic conditions in these areas, neither conventional nor most well known 'alternative' sanitation options are feasible at affordable prices for poor communities or poor governments. A recent study in the region has started to develop a typology of challenging environments for sanitation as a means to: assess the scale of the challenges; understand the specifi c issues involved in improving sanitation; identify, develop or improve sanitation technologies to cope with different environments; and to disseminate the results in the study countries, regionally and beyond.