with the high temperatures we've been having it's simply a limitation of the 'vent out of a window' type system. All that air that's being blown out the vent pipe has to be replaced with outside air (unless you want to suffocate

) so the air being drawn into the room will be hot.
The only use I've found for them is to have the cold air blow directly onto you - at least that way you get some benefit. Other than that, buy a proper split unit aircon where the condensor is on the outside and the evaporator can cool the same air in the room without actually removing it.
Kevin W.
PS>> No water involved in a Air conditioner (Don't confuse it with a Air Cooler). Air con works the same way as a fridge - refrigerant gas is pumped around a sealed system with a condensor and an evaporator (and a couple more bits). Air is drawn across a large sufrace area condensor and due to the evaporate effect the gas is cooled (In an all in one this hot air is expelled via the vent pipe) Air is then passed over a smaller surface area unit called the evaporator where the air is cooled and passed into the room.