Ammonium is a water pollutant which causes odor problems and tends to increase the nitrite and nitrate concentration in water. However, serious and occasionally fatal poisonings in infants have occured following ingestion of well water shown to contain high nitrite concentration. The aim of this study is to get information about ammonium pollution in the community. The water samples were taken from community water wells in 5 Kelurahans in Jakarta: Sunter, Cipinang, Mang-garai, Kampung Kapuk and Klender. The results showed that 65% from 40 samples of water wells were polluted by ammonium and the highest is 25,84 ppm in Manggarai, South Jakarta area.