Access to sufficient amounts of clean water is both a fundamental human need and right. Yet, more than 1 billion people worldwide can not access clean water and 2.6 billion people live without adequate water sanitation (UNDP 2006). Improving the access of poor people to water has the potential to make a major contribution towards poverty eradication. In Lao PDR where 78% of the population is rural, many inhabitants are likely to be exposed to water quality-related hazards due to lack of access to potable water and/or water sanitation. In this context, this study focuses on stream water quality along a Mekong tributary that flows within a mountainous, composite land-use catchment of northern Lao PDR. Water quality was found to vary greatly depending on (i) the location along the stream (ii) the prevailing rainfall conditions and (iii) stream flow conditions. Overall, water quality reflected the balance between the stream self-cleaning potential and human pressure on the riparian zone. Besides these human induced pollutions we also noted spontaneous enrichments in metals in swampy areas fed by dysoxic groundwater. Based on our survey, we propose recommendations to improve or maintain stream water quality and for environmentally friendly management of surface water resources in the uplands of northern Lao PDR.