AbstractBy diluting a boggy water there is produced water with a COD‐Mn of 3.4 … 10.6 mg/l O2which is due only to humic substances. The water is mixed with 2.5 … 12.9 mg/l Cl2at pH‐values of 5.2 … 8.5 and incubated for 24 h at 20°C. CHCl3concentrations of 38 … 480 μg/l were found by the subsequent gas‐chromatographic determination. The production of chloroform can be calculated by means of a quadratic polynomial in dependence on COD‐Mn, chlorine concentra