Abbreviations: Br-DPBs (brominated disinfection by-products); CHBr 3 (bromoform); CHCl 3 (chloroform), CHCl 2 Br (dichlorobromomethane), CHClBr 2 (dibromochloromethane); Clf (free residual chlorine); NPOC (Non Purgeable Organic Carbon); PCA (Principal Component Analysis); T water (temperature of water); T air (temperature of air); TTHMs (total trihalomethanes = sum of THM-4); Abstract Water and air quality of eight seawater swimming pools using chlorine disinfection was measured during four sampling campaigns, spread on one full-year, and in four thalassotherapy centres located in Southeast of France. Concentrations of trihalomethanes (THMs) in air and in water as well as concentrations of parameters, including non purgeable organic carbon (NPOC), free residual chlorine (Cl f), pH, Kjeldhal Nitrogen (KN), salinity, conductivity, bromide ions and, water and air temperature, were measured. Water and air samples were collected in triplicates morning-at the opening of the pools-, noon and night-at the closing of the pools-, in summer and winter. Data analysis was performed by Principal Component Analysis (PCA) and rotated component matrix, from both data quality and other parameters such as TOC, aromaticity (UV 254), pH, hygrometry, and free residual chlorine (Cl f). This statistical analysis demonstrates a high correlation between TOC, Cl f and UV 254 and THM levels found in air and water, particularly for the major ones (CHBr 3 in water : 300.0 µg.L-1 mean, 1029.0 µg.L-1 maximum; CHBr 3 in air : 266.1 µg.m-3 mean, 1600.0 µg.m-3 maximum, and CHClBr 2 in water: 18.9 µg.L-1 mean, 81.0 µg.L-1 maximum; CHClBr 2 in air : 13.6 µg.m-3 mean, 150.0 µg.m-3 maximum). These high levels of bromoform (CHBr 3) are particularly worrisome in such health institutions, even these levels do not exceed the Permissible Exposure Limit (PEL) of 5 mg.m-3 as an 8 hour time-weighted average currently 2 fixed by various administrations, such as Occupational Safety and Health Administration (OSHA).