Abstract: An apparatus for preparing water from water-containing gases released in a conversion device for converting chemical energy into mechanical energy, comprising: at least one membrane which is adapted to at least partly allow passage of water molecules and substantially prevent passage of other molecules; a passage for guiding the waste gases along a first side of the membrane, a discharge pipe arranged on the second side of the membrane for discharging the water released on the second side of the membrane. The conversion device for converting chemical energy into mechanical energy is formed by a conversion device with external combustion, and the discharge pipe are formed at least partly by auxiliary equipment associated with the conversion device with external combustion.