Small water systems confront difficulties providing safe drinking water. Throughout history, small systems have been neglected from provision services, such as water access and feasible treatment technologies. Environmental and geographical factors play a role, but also social factors can influence this discrepancy resulting in social inequalities. Sometimes, government interventions can aid in the relief of these inequalities and sometimes they can be the main cause. Overall, any intervention to small water systems should include a previous analysis of their necessities and characteristics. In Puerto Rico, small water systems are failing in complying with federal and state regulations mainly due to failure in providing an adequate treatment. Slow sand filtration is an adequate technology that can be used in these systems to assure the provision of safe drinking water. In this study it was showed that pre -- treatment with coarse gravel filtration is an effective stage to alleviate inconsistent quality of the influent water of slow sand filters. The design of slow sand filters includes characteristics of the filtration media that are not well defined, mostly in terms of the effective size and uniformity coefficient of the sand. In this study, an evaluation of nine combinations of these two factors was completed in terms of the efficiency of treatment. Smaller effective sizes provided a higher efficiency removing turbidity and total coliforms from the raw water. The effect of the uniformity coefficient was not evident, mainly due to malfunction of the filters in the operation period. Further research should include larger number of replicates to evaluate the interaction of these two factors when taking into account filtration efficiency. Multi stage filtration was evaluated using a filtration system adaptable at the scale of a small water system in Puerto Rico. The system was efficient improving water quality in terms of turbidity and acid forming bacteria. The cost of the system was not comparable with similar market technologies, such as the BioSand filter, but downsizing the diameter of the system can result in a more cost -- effective system. Further research should include this new design characteristics to evaluate the efficiency of the system.