The effect of UVA (300–400 nm), UVB (260–340 nm) and UVC (254 nm) wavelengths on absorbance spectra, dissolved organic carbon (DOC) levels, molecular size distributions, bacterial regrowth potentials (BRP) and trihalomethane formation potentials (THMFP) of aquatic natural organic matter (NOM) from a number of sources was examined to ascertain the use of photooxidation for the removal of NOM from drinking water. Differences were observed in the normalised UV spectra of the NOM samples, and UVC-irradiation resulted in the largest reduction in absorbance at 254 nm and DOC levels. The various UV wavelengths appeared to reduce the molecular size in a similar fashion with sequential degradation from high molecular weight to low molecular weight by-products. Treatment by UVA-, UVB- and UVC-radiation also resulted in increased BRP for all NOM samples. The THMFP of the UV-treated NOM samples HV MIEX and HV Raw appeared to be dependent on the characteristics of the NOM sample and the UV dose. The THMFP of UVA- and UVB-irradiated HV MIEX increased and an initial increase was observed for UVC-irradiated HV MIEX before decreasing with further treatment, while UVC-irradiated HV Raw showed decreased THMFP for all treatment times.