I hate to dispel a long standing belief (actually, that's a lie - I actually enjoy dispelling old beliefs), but caffeine has no more of a diuretic effect than plain old water. All fluids, consumed in quantity, are going to have a naturally mild diuretic effect just as a result of increased fluid volume. Too much fluid can have a diluting effect on anything consumed as well as creating electrolyte imbalances which could effect kidney function etc. Just my layman's opinion. Take it for what it's worth.
