The invention discloses a water heater, and belongs to the technical field of water heaters. The inner end of the water heater is provided with a vacuum heat insulation board between an end socket anda shell, the vacuum heat insulation board is arranged in the weak heat preservation area at the end of the water heater, the occupied space is small since the vacuum heat insulation board is thin, the requirement for small size development of the water heater is met, the heat insulation performance of the vacuum heat insulation board is good, and the heat preservation effect of the water heater is improved. A heat preservation box is fastened to the shell, and the vacuum heat insulation board is located in an inner cavity of the heat preservation box, the vacuum heat insulation board is protected by the heat preservation box, the vacuum heat insulation board is prevented from being bumped and worn without affecting the heat preservation performance, and the service life of the vacuum heatinsulation board is prolonged.