NOVELTY - The system for generating water droplets useful as water for growing plants, comprises a vessel (10), which is placed in atmosphere and has an opening portion (10a), an opening/closing valve (11), which opens the opening portion when ambient temperature is lower than a predetermined temperature or when humidity is higher than a predetermined humidity and closes the opening portion when ambient temperature is higher than the predetermined temperature or when humidity is lower than the predetermined humidity, and a moisture absorbent member (12).    USE - The system is useful for generating water droplets, which are useful as water for growing plants, as drinking water for domestic purposes and for other purposes e.g. for semiconductor manufacturing process.    ADVANTAGE - The water droplet generating system is capable of continuously generating moisture thus enabling continuous supply of water droplets and acceleration of the growth of many plants, increasing yields of the agricultural crops without pumping up the groundwater and saving of labor in watering plants, can provide clean drinking water having no salt content, eliminates the need for clarification of water and for transport from a distant place so that water for domestic use is available at a relatively low cost, and can produce large amount of moisture during daytime.    DETAILED DESCRIPTION - The system for generating water droplets useful as water for growing plants, comprises a vessel (10), which is placed in atmosphere and has an opening portion (10a), an opening/closing valve (11), which opens the opening portion when ambient temperature is lower than a predetermined temperature or when humidity is higher than a predetermined humidity and closes the opening portion when ambient temperature is higher than the predetermined temperature or when humidity is lower than the predetermined humidity, a moisture absorbent member (12), which is housed in the vessel and is constructed to absorb and release water vapor depending on a change of humidity, a condenser portion (14), which is disposed to communicate with an inside of the vessel and is constructed to cool water vapor and condenses water vapor released from the moisture absorbent member at a dew point of water vapor or less to generate a water droplet, timer means for ON and OFF of power supply to a motor at a predetermined opening time, at which temperature rises in a day, and at a predetermined closing time, at which temperature falls in the day, a water reservoir that stores the water droplet generated in the condenser portion, an air introduction channel that communicates the condenser portion with the atmosphere, a humidity sensor that detects humidity in a vicinity of the air introduction channel, a pump that supplies atmosphere, which is introduced through the air introduction channel to the condenser portion, another opening/closing valve that opens and closes the air introduction channel, a controller portion that operates an opening/closing control of the opening/closing valve and an activation of the pump, a moisture transfer member that diffuses the water droplet, which is generated in the condenser portion in soil, clarifying means for clarifying the water droplet generated in the condenser portion, and a water absorbent member, which is housed in the vessel and is constructed to absorb and release the water droplet in air depending on the change of temperature, and a water droplet collecting member, which is placed below the water absorbent member and collects the water droplet released from the water absorbent member. When the opening/closing valve opens the opening portion, the moisture absorbent member absorbs water vapor in atmosphere, and when the opening/closing valve closes the opening portion, the moisture absorbent member releases water vapor. The opening/closing valve opens and closes the opening portion by using a wax and by using a motor powered by a solar battery. A volume of the wax changes depending on a change of temperature. The opening/closing valve is constructed to open at the predetermined opening time and to close at the predetermined closing time. When humidity detected by the humidity sensor exceeds a predetermined value, the controller portion opens the opening/closing valve and activates the pump. The condenser portion is a heat exchanger, which is placed in soil and is constructed to perform heat exchange between soil, atmosphere or water and water vapor released from the moisture absorbent member. The moisture absorbent member is made of mesoporous silica, which has a pore size of 1-7 nm. The vessel and the condenser portion are connected by a connector that is constructed to permit water vapor and to pass between the vessel and condenser portion and is made of a material having a heat conductivity lower than a heat conductivity of the vessel and condenser portion. The vessel has an upper surface that is made of an upper-side member having translucency. The upper-side member includes two plate-like members that define a hermetically sealed space. The water droplets are collected by the water droplet-collecting member. An INDEPENDENT CLAIM is included for a method for generating a water droplet by using the water droplet generating system.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view illustrating a cross-sectional structure of a water droplet generating system.    Vessel (10)    Opening portion (10a)    Opening/closing valve (11)    Moisture absorbent member (12)    Condenser portion. (14)