Thiamine is a water-soluble vitamin necessary for all species survival and it is produced in the aquatic environment by bacteria, phytoplankton, fungi, and archaea. Species of higher trophic levels rely on a continuous uptake of thiamine since they are unable to produce it themselves. Currently, scientists are unaware of how the particulate and dissolved pool of thiamine is regulated. Thiamine related compounds are precursors found in aquatic surroundings used by organisms to synthesise particulate thiamine. In this study, dissolved and particulate thiamine in sites in fresh- and marine water were analysed and tested if the different forms of thiamine related to a set of water-chemistry parameters. The results showed a correlation between the thiamine related compounds amino-5-hydroxymethylpyrimidine (HMP), 5-(2-hydroxyethyl)-4-methyl-1,3-thiazole- 2-carboxylic acid (cHET), 4-methyl-5-thiazoleethanol (HET) and conductivity. The conductivity could be explained by the difference in salinity between the systems. Thiamine related compounds showed no correlation towards particulate thiamine. There were also no significant differences in thiamine related compounds between aquatic systems. The dissolved and particulate pool of thiamine can be explained by the phytoplankton community composition since different species contribute to thiamine pools differently depending on their thiamine cycle. Future research should focus on understanding the thiamine cycle between the different pools.