Helicobacter pylori causes probably the most widespread infection among the world population (>50%). This infection evolves towards diseases like chronic gastritis but it is difficult to apply prevention schemes because the routes of transmission are yet unclear. The epidemiological studies done so far point to the existence of two routes: person to person; and, through contaminated water. This second route considers H. pylori as a waterborne pathogen. The molecular detection techniques such as PCR are providing the technical tools to study these microorganisms in the aquatic environment. The objective of this work was to study the possibility of using a seminested PCR to know the incidence of H. pylori in sewage water of the Northeast of Spain. A PCR method designed to detect Helicobacter pylori from gastric biopsies (Clayton et al., 1992) was adapted to water samples. Amplification conditions were modified, and a second DNA amplification was added. This optimized method was applied to detect H. pylori from sewage. A total of 12 sewage samples were analyzed from which 7 were positive. It shows that Helicobacter pylori is present in this type of polluted water. These findings support the view that the Helicobacter pylori is present in polluted water and, therefore, these pathogens have to be monitored from water in order to avoid its spreading. Includes 8 references, tables, figure.