It is possible to enrich HTO in water by electrolysis of the water to produce hydrogen and oxygen gases. In this process, water containing the lighter hydrogen atoms 1H and 2H are preferentially removed from the water, leaving an electrolyte which is increasingly enriched in HTO. Starting with a volume of 250 mL, it is possible to reach an enrichment factor of 25-35, depending on the equipment and procedure used. However, in all cases where HTO is added artificially as a tracer to water, there is not much gain in this enrichment technique because the natural HTO content is increased, as well as the background. Thus, the quality of the analysis is not improved even though the number of counts increases. Sample enrichment is indispensable when analysing natural samples that have low contents of tritium, however.