Based on spectra of peat water samples representing a range of geochemical origin from minerotrophic fens to ombrotrophic bogs, dissolved organic carbon (DOC) was only weakly predicted (r2 = 0.710) by absorbance at 330 nm. Differences in molecular weight fractions in the dissolved organic matter apparently did not affect the correlation. Major improvement in the predictive power of absorbance at 330 nm was produced by inclusion of the Fe content of the peat water (r2 = 0.962), which can be determined simply as o‐phenanthroline reactive Fe. Dichromate‐oxidizable organic C was also predicted well from absorbance at 330 nm.