Within Nairobi, informal settlements occupy roughly five percent of residential land yet house more than sixty percent of the population a figure projected to double within fifteen years in one of Africa’s urbanising capitals. This study is positioned in the tension between that growth and the basic services meant to absorb it. The WASH profile is stark. Households here have markedly lower access to safe drinking water and consistently fail national sanitation standards. Communal facilities, where they still exist, are shared among hundreds and break during heavy rains; menstrual hygiene services are, for most women and girls, absent or improvised at personal cost. Sustainable Development Goal 6 commits the international community to adequate, equitable WASH for all by 2030. In developing-country contexts, however, Kenya’s slum-upgrading targets remain uneven outside formal land-use planning, widening the gap between city metrics and household experience. Climate variability heavier rains, prolonged dry spells, and flash floods in low-lying settlements further destabilises these fragile systems, contaminating shallow wells and destroying pit latrines. Women and girls bear the heaviest burden, often managing menstruation without safety or dignity. Children, meanwhile, face developmental risks extending well beyond infrastructure gaps. Yet the story is not solely one of crisis. Across the city, residents, community organisations, and local utilities have piloted community water kiosks, container-based sanitation, women-led menstrual-hygiene cooperatives, and school WASH clubs — responses that show how services can be delivered in dense, low-income urban areas. Against this background, the study examines water, sanitation, and menstrual hygiene in selected informal settlements of Nairobi, linking household-level evidence with SDG 6 indicators. It aims to inform WASH interventions that are both locally grounded and nationally relevant, with implications for Kenya’s SDG 6 trajectory.