This thesis describes a systematic laboratory and field study of arsenic and iron removal from contaminated groundwater by oxidation-coagulation at optimized Ph(OCOP) technique. Sodium hydrooxide (NaOH), Nitric Acid (HNO3) and ferric chloride (FeCL3) were choosen as pH conditioner,oxidant and coagulant respectively.The thesis has been organized in four chapters dealing with different aspects of the study as follows: Heavily arsenic-contaminated drinking water can be found in Mexico, Chile and India. The most serious situation occurred in Bangladesh, where the drinking water can contain 500-1000 μg/L arsenic. The high amount of arsenic content of the groundwater is a problem in Hungary too. The problem covers Baranya, Borsod-Abaúj-Zemplén and Jász-Nagykun-Szolnok counties, but especially the area of the Great Planes: Bács-Kiskun, Békés, Csongrád, Hajdú-Bihar and Szabolcs-Szatmár-Bereg Counties.