In various natural sources of surface water in Ecuador, as well as in others worldwide, the concentration of arsenic exceeds the permissible limits (10 μg / L) established by the World Health Organization. The objective of these investigation was to determine the levels of arsenic in surface water and sediments in the Carrizal river basin (Manabí, Ecuador), an area that has an important agricultural activity. 21 stations in three areas were monitored, covering an area of 51 km. Arsenic concentrations in water and sediment were evaluated by means of atomic absorption spectrometry with the PerkinElmer® AAnalyst ™ 200 kit, in accordance with the guidelines of Standard Methods Edition 2015, by the APHA AWWA WEF 3114- B methodology. The experimental design of random blocks was applied, with a factorial arrangement of the three sampling areas. The indicated results are found for arsenic o...