The crystal structure of the pristine (I) and aged (II) crystals of CH3NH3PbI3 (hereafter MAPbI(3)) hybrid organic-inorganic lead iodide has been studied at 293 K with high-precision single-crystal X-ray diffraction using a synchrotron light source. We show that (I) and (II) are characterized by an identical tetragonal unit cell but different space groups: I422 for (I) and P4(2)2(1)2 for (II). Both space groups are subgroups of I4/ mcm, which is widely used for MAPbI(3). The main difference between (I) and (II) comes from the difference in hydrogen bonds between the MA(+) cation and the PbI3 framework which is the direct consequence of H2O insertion in the aged crystal (II).