Pollution of well water with arsenic has been revealed in many regions of the counhy. This is a danger for the health of population causing many dangerous diseases including cancer in digestive organ. In order to determine the polluted regions as well as pollution level of each region the Center for Environmental Technologies and Sustainable Development (CETASD) belonging to Hanoi National Universities has carried out analysis of well water samples collected from 15 provinces within Red River Delta. The findings showed that the pollution is serious in the provinoes located between the basin of the Red River and Day River.