A highly selective molecularly imprinted polymer (MIP) for the recognition of the pesticide carbaryl in water has been synthesized using halogenated bisphenol A compounds as one of the polymeric precursors and carbaryl as the template molecule. On the basis of the heavy-atom effect, both the brominated and the iodinated MIPs allowed analyte detection by room-temperature-phosphorescence measurements. In the presence of an oxygen scavenger (sodium sulphite) the halide, included in the polymeric structure, induced efficient room-temperature phosphorescence of the analyte (once it had been selectively retained by the MIP). The MIP cavity can be easily regenerated for subsequent sample injections with 2 mL methanol. The optosensing system developed has demonstrated high selectivity for carbaryl, even in the presence of other luminophores that could be unspecifically adsorbed onto the MIP surface. Under optimal experimental conditions, the detection limit for the target molecule was 4 microg/L (3-mL sample injection volume), and the linear range extended up to 1 mg/L of the analyte. Good reproducibility was achieved (a relative standard deviation of 3% was obtained for ten replicates of 150 microg/L carbaryl). The synthesized sensing material showed good stability for at least 3 months after preparation. Finally, the applicability to carbaryl determination in real samples was evaluated through the successful determination of the pesticide in spiked mineral and tap water samples.