The purpose of this study is to identify the chemical composition of corrosion material accumulated on the inner wall of a mild steel ''water pipe'', and the iron species present. It will be shown that the material accumulated is predominantly derived from in situ iron corrosion processes rather than from the sedimentation of particles introduced into the water distribution system. The dominant iron species found was Fe(III) - >90%, with concentrations of Fe(II) and Fe f r e e + a m o r p h o u s (free and amorphous Fe) being <10%. The results also showed that the accumulated material was composed predominantly of goethite (α-FeOOH - 75.6%), with magnetite (Fe 3 O 4 - 21.5%) and lepidocrocite (γ-FeOOH - 2.9%) also being present. It is assumed that FeOOH is derived from amorphous Fe(OH) 3 when it dehydrates.