Sembiring, H. .; Br Karo, M. . Test the Capability of the Down Flow-Up Flow Combination Filter Rate Lead (PB), Iron (FE) and Manganese (MN) Which Are Contained on Water Well Drill Public Residential Still Village Ndokum Siroga I Subdistrict Intersection Four Regency Karo . ijmst 2023, 10, 2348-2354.