Water is a very valuable asset for human life, but quality drinking water is becoming scarce due to the presence of contaminants. Disinfection by-products (DBPs) such as chlorine are commonly formed in water treatment plants due to the processes involving disinfectants, which can result in the formation of parabens-related DBPs (p-DBPs), which have a higher impact on human health than the parent compounds. The presence of biofilms in drinking-water distribution systems is unavoidable, but scientific knowledge on the effects of parabens and their p-DBPs on microbial communities is scarce². Strains of Stenotrophomonas maltophilia isolated from drinking-water distribution systems in Portugal were used to assess their behaviour in planktonic and biofilm states (using polyvinyl chloride–PVC as an adhesion surface) after exposure to Methylparaben (MP), Ethylparaben (EP) and p-DBPs such as para-hydroxybenzoic acid (pHBA), 3,5-dichloroethylparaben (3,5diClEP), and 3,5-dichloromethylparaben (3,5diClMP) at 50ng/L. The biofilms were analysed for culturability using CFU, cell density using DAPI, and EPS content using polysaccharides and protein quantification. Planktonic analysis was carried out in the presence of parabens and p-DBPs over 24h at 610nm. pHBA increases the number of polysaccharides (10.5µg/cm²), followed by EP (10.37µg/cm²) and MP (9.98µg/cm²). PHBA also raises the amount of protein (6.5µg/cm²), but it remains less than EP and MP (7.07 and 8.01µg/cm², respectively). 3,5diClMP and 3,5diClEP show decreased polysaccharides but increased proteins, with 3,5diClEP having the highest protein content (16.6µg/cm²) and a significant cell density reduction (-0.07 log cells/cm²), followed by pHBA. In planktonic mode, parabens boost bacterial growth; biomass rises ~30%, and growth rate ~10%. 3.5diClMP and 3.5diClEP undergo more significant changes than their parent compounds. This is concerning, given that they are produced during chlorine water treatment. Paraben exposure affects biofilms of S. maltophilia isolated from drinking water, especially in planktonic form, which raises concerns about the potential threat to the quality and safety of drinking water.