joggerjayne, sorry but that's cobblers. The tiny diuretic effect of tea, coffe and alcohol is far outwieghed by the volume of liquid they comprise. If not then those who only drink tea and coffee would shrivel up and die! ALL intake of liquid is valid, whatever the form.
This was confirmed on QI, where a senior dietician from a London hospital was consulted about this very subject and gave her professional view (that what you said is rubbish). She also said there is no fixed amount you should drink each day - just drink when you are thirsty, the body is clever enough to know when it needs hydration - hence thirst!!