SBR- Content.pmd - INBO

12 - Domestic water and sanitationfrom sediments into groundwater, and in particular, the influence of human activities (such asintensity of water use) on the process, are not yet clearly understood however, making exactpredictions difficult.What is clear from surveys so far is that arsenic is likely to be a significant future problem inCambodia, Lao PDR and Viet Nam (the position in Thailand is less clear). However, becauseimproved wells have been developed more recently in the Mekong countries, the use of potentiallyarsenic-contaminated waters may have been less universal and for shorter periods than in someother countries at risk. Therefore, if timely and appropriate action is taken by governments andtheir external supporters (including identification of alternative drinking water sources for theaffected wells – or failing that, appropriate treatment of the water), the associated health problemsneed not be as serious as they have been elsewhere.While arsenic in groundwater remains a serious issue for the LMB, it must also be set within thebroader water quality context. Risks must be balanced with those of widespread microbialcontamination of many traditional sources, and excess fluoride in others - both of which alsohave major health impacts. 10Source: After WHO 20023.2.3 Contamination of surface waterDeforestation leads to land degradation, soil erosion and increased sediment content in surfacewater, and raises the cost of water treatment. So does flooding, if it increases the organic content inwater supplies. Coal mining, oil exploration and gem mining can increase turbidity in surface watersand also pollute them with toxic chemicals. These impacts are exacerbated by lack of monitoringand enforcement.Natural erosion and that induced by human activity may expose toxic rock. For example, toxicaluminium compounds have been eroded from rock in western Cambodia. Construction of dams,roads and other infrastructure may contaminate drinking water sources directly with wastes, orindirectly by exposing toxic bedrock to erosion. Residues from past warfare are another un-assessedsource of contamination, as is leechate from solid waste disposal sites, especially sites with hazardouswastes.Pesticides could become a concern in future if their use increases as agriculture intensifies in theLMB. They can contaminate surface and groundwater through run-off after application, whenirrigation water returns to watercourses, and when agricultural equipment is washed. In addition todamaging ecosystems, pesticides threaten humans both by contaminating domestic water suppliesand by concentrating in the fish and other aquatic animals that humans eat.Increasing use of fertilisers is also a potential problem, raising levels of nutrients in the delta inViet Nam, for example. This may cause eutrophication and an explosive growth of algae. Algalblooms are a threat not only to fish, but some forms are also highly toxic to humans. However, arecent study 11 identified only a moderate risk of human waste and fertiliser triggering surfacewater algal blooms downstream from Phnom Penh. On the other hand, the potential increase innitrate/nitrite levels in groundwater, particularly in areas where fertiliser use is extensive, needsto be monitored.251