## 1 Introduction  
Water quality and accessibility are critical issues affecting millions worldwide, particularly in rural and resource-limited environments in developing countries. Some Maasai communities in northern Tanzania face severe water quality and scarcity problems that significantly impact the health and living conditions of the local population. Contaminated water sources lead to various health issues, including waterborne diseases, a major cause of morbidity in these regions [1]. Advanced water treatment technologies are often not feasible in these settings due to the lack of infrastructure and financial resources [1]. Consequently, there is an urgent need for sustainable, low-cost water purification solutions that can be implemented using locally available materials, adhering to the principles of appropriate technology. Moreover, these solutions must be maintainable by the community, and therefore should not rely on advanced technologies. One promising approach is the use of slow sand filtration (SSF) systems. Here, we present a case study for improving drinking water quality and evaluating the application of an SSF system within a Maasai community in northern Tanzania, conducted in 2023. A key innovation of this research is the development of a tailored model that optimizes water treatment systems for off-grid communities, integrating SSFs and sedimentation with coagulant materials, resulting in a compact system designed for household use that effectively addresses high turbidity levels. The Maasai villages are estimated to be spread over an area of approximately 11,000 to 15,000 km\({}^{2}\) in the south of Arusha, located in northeast Tanzania. The Maasai population in this region is roughly estimated to be between 80,000 and 120,000 residents, with children comprising about 30-40% of the population [2; 3]. In the specific area where the delegation worked, most of the villagers' drinking water comes from local sources such as wells (Figure 1) and two local reservoirs dammed by the Red Dam and the Sokoru Dam (Figures 1 and 2a,b, respectively). These dams present significant environmental and health challenges, such as the bacteria, organic matter, and feces that contaminate them due to exposure to local livestock. Aside from boiling, no additional treatment is employed to purify the contaminated drinking water prior to consumption. Figure 2c presents a typical case where livestock herds enter the water and defecate on its banks, leading to contamination. Figure 1: Map of the local water sources [4]. Based on interviews and conversations with residents of the surrounding villages, most of the population tries to consume water from local wells as they are generally of better quality than the dams, with low turbidity and bacterial contamination. Furthermore, most residents understand the importance of clean water and avoid drinking stagnant reservoir water whenever possible. Several factors, including economic, geographical, and social reasons, impact on the limited access to high-quality drinking water. For example, in some areas, residents must pay around 100 shillings ($0.04) for about 20 L of well water, but severe poverty (GDP < 1000 USD) forces some to opt for free reservoir water. Additionally, wells can be far from some homes, making nearby reservoirs a more accessible option. Social dynamics also play a role, as communities may restrict access to well water to meet their needs. As a result, thousands of people are still forced to rely on water from upper reservoirs, such as the Sokoru Dam or the Red Dam (Figure 1). At the beginning of 2023, approximately 300 VF-100 filters were donated by American donors to communities and villages, with priority given to residents of villages lacking reliable, clean water sources. The residents who received these filters underwent thorough training in operation and maintenance. VF-100 filters are used for particle filtration with sizes of up to 0.1 microns and are approved for use by the World Health Organization (WHO).