Dishwashers impact the environment through both their power and water consumption. Energy efficient models can use 
up to 40% less power and cut water usage by up to 25%. Full details of the energy efficiency ratings programme for dishwashers can be found here.
The energy labels on dishwashers are part of the EU plan to help consumers make informed choices when purchasing new household appliances. The label itself will give:-
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A rating from A to G based on the energy efficiency, with an A rated appliance deemed to be the most efficient compared to a G rating as the lowest.
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The energy consumption in kilowatt hours per cycle for one ‘normal’ test cycle (usually the economy or eco cycle)
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The drying and cleaning energy performance, again based on the A to G system, assessed in relation to the capacity of the machine (e.g. 12-place settings)
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The number of place settings and water consumption for the test cycle*
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Some labels will also show the noise level, this is optional at the time of writing.
* The water consumption for other cycles may well be different.
Despite advances in efficient dishwashers many groups claim that hand-washing of dishes is a more environmentally friendly alternative to the use of dishwashers. Manufacturer Electrolux claims that dishwashers can be up to 80% more efficient than hand washing dishes due to recent innovations in dishwashing efficiency (source : Electrolux.com)
In 1995 a dishwasher would have consumed an average of 22 litres of water per load (source: Electrolux.com) yet a Waterwise survey established that the average dishwasher uses between 12 and 16 litres while washing by hand can use as much as 63 litres of water (source: Waterwise).
Innovations such as the Fisher & Paykel DoubleDrawer technology (source Fisherpaykell.com) help increase the efficiency of their dishwashers because you only use the amount of space you actually need and therefore don’t waste electricity unnecessarily.