A heat recovery system for heating water comprises one or more heat exchangers 9 for heating water by exchange with waste heat. A storage reservoir 11 stores the water heated by the heat exchanger(s). The heat exchangers(s) is/are switchable between a first mode of operation in which water is circulated by a pump 12 in a circuit including the storage reservoir and the heat exchanger(s), and a second mode of operation in which water is circulated by the pump in a circuit that by-passes the heat exchanger(s). The water is heated to at least a minimum temperature and supplied to at least one outlet in both the first and second modes of operation. Waste heat may be from a refrigeration system. Switching between modes of operation may depend on water level and temperature of water in the reservoir. The pump may run continuously in both modes. Heat recovery may be from a dairy plant and the heated water used in a wash rinse process without supplementary heating of the water. Other uses include hot water in breweries, wineries, cheese plants, meat and other food processing plants, hospitals, hotels and swimming pools.
