Near infrared diffuse reflectance spectroscopy with a fibre-optic probe was used to determine the water content in ferrous lactate dihydrate. Spectra were recorded by immersing the probe in a beaker containing the ferrous lactate sample. Spectral data were processed by using two different multivariate calibration procedures, viz. stepwise multiple linear regression (SMLR) and partial least-squares regression (PLSR). The results provided by the two calibration procedures were similar and departed by less than 1.5% from the values obtained by Karl Fischer titration.