To increase the concn. of dissolved oxygen, to prevent water from becoming rotten and to always keep water fresh by an apparatus wherein an air jetting pipe is disposed in a vase and a through hole on the bottom part and an air inlet pipe are sealed with a sealing material and a motor-driven air pump is disposed below the vase and an air outlet and the air inlet pipe are connected with each other.

An air jet pipe 3 consisting of an air inlet pipe 3-1, an air outlet pipe 3-2 and a nozzle 3-3 is disposed in a vase 1 and a through hole 1-1 on the bottom part and the air inlet pipe 3-1 are sealed with a sealing material 1-2. In addition, a motor-driven air pump 2 with an electric source plug, a cord and an air outlet 2-1 is disposed below the vase 1 and the air outlet 2-1 and the air inlet pipe 3-1 are connected with each other. Therefore, air is always jetted into water in the vase 1 from the nozzle 3-3 and the water temp. is lowered by decrease in temp. caused by expansion of air to increase the concn. of dissolved oxygen and it is possible thereby to prevent water from becoming rotten and to keep always water fresh.