The compound Cs2[FeCl5(H2O)], has awakened a renewed interest owing to its recent classification as a new linear magneto electric material. This compound orders antiferromagnetically at TN = 6.5 K. The anisotropy of the linear magnetoelectric effect of the K-based and Rb-based compounds is consistent with the magnetic point group m'm'm', already reported in literature (J. Campo et al). However, the magnetic structure of the Cs-based compound has not been reported. Furthermore, we have observed a structural phase transition, which has not been resolved. This structural phase transition is probably caused by the displacement of the Cs counterions at low temperature. High resolution single-crystal neutron diffraction is necessary for explaining the structural origin of this transition in this system as well as for the determination of the magnetic structure both at zero field and under applied magnetic field. In order to fully characterize the nuclear phases and determine the magnetic structure, we ask for 17 days of beam time at D9 single crystal diffractometer.