PURPOSE: To improve the heat collection efficiency by providing a communication passage that communicates upper parts of a hot water tank and a feed water tank so that the differential temperature between the water at a higher temperature and at a lower temperature within the hot water tank may be increased without enlarging the capacity of the hot water tank.

CONSTITUTION: The present solar water heater has a communication passage 13 in the upper part of a partition 5 that communicates a hot water tank 2 and a feed water tank 6. Water that is heated by a heat collector is also directed from the upper part of the hot water tank 2 through the upper communication passage 13 to the upper part of the feed water tank, and, in turn, the cold water in the feed water tank is forced downward. Because of this, the cold water is fed into the heat collector, and so, the heat collection efficiency is improved. Under an overflow hot water supply condition, a stagnant area A would develop in the neighborhood of the partition 5 if there were not the upper communication passage 13. Owing to the presence of the communication port 13, the water in the feed water tank 6 flows in form the communication passage 13 to force the stagnant area A to the side of an overflow port 11, and the water at a high temperature in the hot water tank 6 can be adequately taken out of the overflow port 11.