A cooker comprising: - a cooking chamber; - a food receiving container in the cooking chamber having a permeable bottom wall; - a system to maintain a predetermined level of water in the cooking chamber said water being added to the cooker during cooking to create steam, wherein the predetermined level is disposed between a base of the cooking chamber and the bottom wall of the food receiving container; a heater for heating air in the cooking chamber; and a fan for circulating a flow of hot air in the cooking chamber to cook the food, wherein the heater and fan are arranged to generate steam, by circulating the flow of hot air in the cooking chamber to evaporate the water, wherein said system comprises a reservoir that includes: - a tank configured to retain water at a level higher than the predetermined level due to vacuum pressure acting on water contained in the tank, - a breather in fluid communication with the tank, wherein the reservoir is in fluid communication with the cooking chamber below the predetermined level, and the cooking chamber and the breather are configured so that changes in water level in the cooking chamber are reflected in changes in water level in the breather, and wherein the reservoir is adapted so that air can pass through an opening (36, 40, 50, 60) into the tank from the breather when the water level in the cooking chamber drops below the predetermined level to increase the pressure acting on the water in the tank and displace water from the reservoir into the cooking chamber until the water level in the cooking chamber is restored to the predetermined level. - a cooking chamber; - a food receiving container in the cooking chamber having a permeable bottom wall; - a system to maintain a predetermined level of water in the cooking chamber said water being added to the cooker during cooking to create steam, wherein the predetermined level is disposed between a base of the cooking chamber and the bottom wall of the food receiving container; a heater for heating air in the cooking chamber; and a fan for circulating a flow of hot air in the cooking chamber to cook the food, wherein the heater and fan are arranged to generate steam, by circulating the flow of hot air in the cooking chamber to evaporate the water, wherein said system comprises a reservoir that includes: - a tank configured to retain water at a level higher than the predetermined level due to vacuum pressure acting on water contained in the tank, - a breather in fluid communication with the tank, - a tank configured to retain water at a level higher than the predetermined level due to vacuum pressure acting on water contained in the tank, - a breather in fluid communication with the tank, wherein the reservoir is in fluid communication with the cooking chamber below the predetermined level, and the cooking chamber and the breather are configured so that changes in water level in the cooking chamber are reflected in changes in water level in the breather, and wherein the reservoir is adapted so that air can pass through an opening (36, 40, 50, 60) into the tank from the breather when the water level in the cooking chamber drops below the predetermined level to increase the pressure acting on the water in the tank and displace water from the reservoir into the cooking chamber until the water level in the cooking chamber is restored to the predetermined level.