embodiment of a water tank generally designated by reference numeral 1 for a coffee machine in accordance with the present invention the water tank 1 has a partition wall 2 to subdivide the water tank 1 into a reservoir 3 and a lead container 4 the reservoir 3 fluidly communicates with the lead container 4 via an outlet port 5 in the partition wall 2 the lead container 4 is connected with a pipe of a heating unit 12 via a connection line 6 with integrated insert 13 to define a constriction the lead container 4 includes an opening 14 for fluid communication with the surroundings to thereby effect a same atmospheric pressure in the lead container 4 as in the environment in which the machine operates a valve is disposed in the outlet port 5 to control a supply of water from the reservoir 3 to the lead container 4 in the shown non limiting example of fig1 a the valve is constructed as float controlled valve which includes a float 7 and a closure element 8 this closure element 8 is provided to close the outlet port 5 in the partition wall 2 as soon as a water level h has reached a desired value hs the float controlled valve assumes the function to ensure that the water level h in the lead container 4 is able to fluctuate only slightly about a desired value hs a drop in the water level h in the lead container 4 causes the float 7 of the float controlled valve to move away from the outlet port.