watched from the water flooding hole 15 preventing from adding too much water that the water will overflow from the through hole 13 the body 1 is provided in advance with an assembling port 161 for installing a water level indication unit 16 the water level indication unit 16 includes an outer tube 162 and a ball 163 the abovementioned assembling port 161 is connected to the holding space 11 of the body 1 whereas the outer tube 162 is a transparent tube with a sealed top end and is tightly installed at the assembling port 161 a joining place between the outer tube 162 and the assembling port 161 is provided with a leak proof washer is pasted with silicon or is treated with other known leak proof methods to prevent water from leaking out the top end of the outer tube 162 can be provided additionally with tiny air vents not shown in the drawings to maintain balance between inner and outer pressure of the outer tube 162 an interior of the outer tube 162 holds the ball 163 and the ball 163 is preferably of explicit color to show the water level in the holding space 11 referring to fig1 to 4 after adding water from the water flooding hole 15 into the holding space 11 the water flooding hole 15 is sealed by the cover 151 at this time the ball 163 will ascend as shown in fig3 to show the current water level in the holding space 11 whereas as the porous rod 2 is.