Researchers studied how to remove iron, manganese, and ammonia from water using a special filter. They found that increasing the flow rate of water through the filter can help lower the levels of these pollutants. By adjusting the flow rate, the filter can meet the National Drinking Water Standard for iron, manganese, and ammonia concentrations. The depth of the filter needed to meet the standard varies depending on the pollutant, with manganese requiring a deeper filter compared to iron and ammonia.