In Nicaragua, active research for arsenic started in 1996, after the first case of arsenic poisoning was reported in a rural community. Arsenic concentrations present in drinking water cause chronic poisoning, which depending on the exposure, lead to several life-threatening long term effects. It is however unknown to what extent this contamination is spread over the country, since many water sources have not been tested for arsenic. Different arsenic mitigation techniques have been implemented, like the Kanchan filter, but long-term field performance of such techniques are unknown and little follow up research has been done. The overarching goal of The Arsenic Project (TAP) is to contribute to the ongoing research in arsenic contamination by developing social and technical guidelines for rural households to mitigate arsenic exposure risk in selected areas of Nicaragua. This is declined in this report under the following three research components: risk, technical and social, with the end objectives to measure the arsenic concentration in wells, to calculate the related exposure risk, to map high risk areas (hotspots) and to assess the performance of Kanchan filters or more generally water treatment technologies encountered both from a technical and a social perspective. Arsenic concentrations were measured using the Arsenator®, along with several water quality parameters (pH, temperature, conductivity, etc.) using a multimeter. Arsenic speciation between As(III) and As(V) was done using the Clifford method. Short interviews were conducted to know more about the well’s characteristics (age, number of user, etc), water-related habits, and characteristics of household technology solutions, when applicable. In the latter case, assessment of the filter performance (flow rate, arsenic removal rate, etc.), and an inquiry of maintenance was done. Semi-structured interviews, focus group and in-depth interviews were used to qualitatively assess the perception of water-treatment technologies, the awareness about (arsenic) contamination and the willingness to invest in freshwater supply. TAP investigated in 5 municipalities, with at least 3 communities within each of these municipalities, cumulating more than 4000 km. 128 wells have been sampled, from which 38% contained arsenic. In 7% of all the wells, As(III) was found. Arsenic concentrations, excluding zeros, ranged from 3 to 267 ?g/L (upper bound measured in the municipality of Telica). From all the sampled areas, most contaminated wells were found in Larreynaga, Telica and Muy Muy. In general, highest arsenic concentrations were found in wells with high temperature and high conductivity. The main arsenic mobilization mechanism is most likely geothermal influence, but possibly also reductive dissolution. In total, six Kanchan filters were found. Only one Kanchan filter has a sufficient removal efficiency and the others remove nothing, have a poor removal capacity (9%) or increase the arsenic concentration during filtration. The one removing arsenic also has the lowest filtration rate. Fragility of components (tap, clay-pot), lack of pre- and post-support were recurrent in filter’s limitations. Social acceptance of the filter is generally high and users have faith in its removal capacity. In general, arsenic is seen as a threat, but arsenic awareness differs a lot depending on the community history (previous campaigns) or personal contacts with the municipality or NGOs. Other arsenic mitigation strategies are also researched and implementation of relatively complex mitigation strategy was observed to be performing successfully. General guidelines and recommendations for arsenic mitigation strategies are formulated in the report. In particular, the development of an integrated mitigation solution is community-specific and time dependent (short term vs. long term). If filters are selected a viable solution, it is important to make sure that the removal efficiencies are sufficient and for a long duration, users are confident about the filter efficiency, and that a good support program before, during and after implementation exists.