This research emerged from the need to improve the Netherlands’ contribution to international water and sanitation service delivery. Over the previous two decades these serviced were not found to be sufficient sustainable according to the Dutch Ministry of Foreign Affairs (2013). This thesis researches how development aid organisations can contribute to sustainable WASH services by looking to the strategic planning process. In this research an adaptive planning approach is designed to contribute to long-term sustainable WASH services. It is a systematic step-wise pro-active approach where planners need to think beforehand of ways a plan might fail and design adaptation actions to guard against such failure. An adaptive planning approach has been adapted for sustainable WASH services and consist of three systematic steps:(1) defining the impact and critical assumptions of the WASH programme, (2) defining relevant uncertainties by using contextual scenarios, and (3) defining adaptation actions and the timing of the actions. The content and the applicability of the adaptive planning approach for long-term sustainable WASH has been examined during this research in the context of Bangladesh. To examine the approach a single case study is used. In this research multiple research methods have been applied to improve the reliability and validity of the findings, but also to capture different perspectives on this topic. First by means of an adaptive planning workshop in the Netherlands with WASH experts from the Dutch NGO Simavi and sequential by means of a field-research in Bangladesh, including interviews with local project stakeholders and field-trips. It can be concluded that WASH experts in the Netherlands and the project stakeholders in Bangladesh reacted differently on the three systematic steps of the adaptive planning approach for sustainable WASH. The indirectly involved project stakeholders - WASH experts - found it easy to question project assumptions and to identify critical assumptions for the project failure but could not propose specific adaptation actions. The directly involved project stakeholder - local project stakeholders in Bangladesh - found it more difficult to criticize and reassess project assumptions, but they defined feasible adaptation actions. It can be argued that ‘misrepresentation’ of critical assumptions of the project created hazard to all sequential steps of the adaptive planning approach for long-term sustainable WASH services. Purposely defining scenarios of success and gloss over the potential for failure, conflicts with the pro-active adaptive planning approach to define adaptation actions at the begin of the project. Therefore, it is questionable whether all systematic steps of the approach serve the interest of all project stakeholders. This makes that the adaptive planning approach, as it is designed now, does not contribute to long-term sustainable WASH services in environments where project incentives are on benefits and not on robustness. Based on the findings of this research, it can be recommended that different components of the adaptive planning approach for long-term sustainable WASH services should be practices by different involved parties.