The World Health Organization (WHO) estimates that around ~ 150 million people in 70 different countries have been consuming water with arsenic levels higher than the recommended limit of 10 µg/L. Here we describe the concentrations of inorganic arsenic in drinking water in homes of pregnant women living in the province of Tacna, near the southern border of Peru. 161 pregnant women were enrolled in their second trimester of pregnancy. A total of 100 mL drinking water was collected in each household from the source of most common use. Inorganic arsenic was categorized into three levels with a commercial kit. Thirty percent of women had drinking water ≤ 10 µg/L (the WHO recommended level), 35% had 25 µg/L, and 35% had greater than 50 µg/L. Low arsenic levels were found in the southernmost homes, supplied by groundwater, while high levels were found in the northern and metropolitan homes supplied by river water.