Predicting the impact of SDG 6 on forests and forest people requires a balanced understanding of the relationship between forests and water. Notable aspects are that forest cover reduces annual runoff but correlates well with water quality, and that recycling of evapotranspiration from forests is important for downwind precipitation. Within this context a target-by-target review of SDG 6, informed by South American examples, suggests that the Goal is unlikely to exert a major influence on forest cover. Targets 6.1 and 6.2 concerning water and sanitation provision will have relatively little impact on forests except through a demand for hydrological ecosystem services and the use of wastewater in forestry. Within the four water resources targets (6.3–6.6) significant impacts may be limited to water efficiency considerations (Target 6.4) restricting plantations in water-stressed areas and Integrated Water Resources Management (Target 6.5) driving a more integrated view of catchments and their management. The eventual SDG 6 impact will depend on the context of water–forest relationships (illustrated using the Hindu Kush Himalayas as an example), the extent to which SDG 6 will in fact be implemented and alignment of the Goal with forest policies, based on a landscape approach.