A total reflection X-ray fluorescence method was developed to ascertain the absence of indium at a concentration level of >1 ng/mL in heavy water samples. A continuum strip in the energy range of 25–35 keV was used for sample excitation and In K_α was used as analytical line. The detection limit for indium, obtained after preconcentration and continuum excitation, was found to be 1 ng/mL with a sample size of 2μL. A heavy water sample was analysed for indium using this approach.