It’s official, running a fully loaded dishwasher uses less water than washing dishes by hand. If you use an Energy Star rated dishwasher you will save even more. An replacing an older dishwasher with a newer Energy Star rated dishwasher can save you about $30 dollars a year in energy costs too.
According to Frigidairee appliances:
If you still wash your dishes by hand, you’re probably wasting more than just your valuable time. Over an average eleven-year lifespan, Energy Star qualified dishwashers can save 55,000 gallons of water (that’s a lifetime supply of drinking water for more than four people) or $465 in energy and water bills (that’s like getting a 15-year supply of dishwasher detergent).

Here are some additional savings that come with upgrading to an Energy Star dishwasher:

Save Time:
Using an Energy Star qualified dishwasher instead of handwashing will save nearly 10 days of your time each year. So stop scrubbing – just load and go!
Dishwashers today don’t require pre-rinsing of dishes before loading. Pre-rinsing doesn’t necessarily improve cleaning and wastes water. Just scrape off food and liquids – the dishwasher will do the rest.

Save Money:
Cut your energy and water bills by more than $40 per year compared to handwashing.
You can save $465 in energy and water bills over the life of an Energy Star dishwasher compared to washing dishes by hand.

Save Energy:
Use half as much energy as washing by hand.
Fill your dishwasher to full capacity to get maximize the energy used to run it. Most of the energy used by a dishwasher goes to heat water. Since you can’t decrease the amount of water used per cycle, fill your dishwasher to get the most from the energy used to run it.

Save Water:
Use nearly 5,000 gallons less water per year, compared to washing dishes by hand.
Run your dishwasher only on the cycle necessary for the task to conserve water

Reduce Noise:
Energy Star qualified dishwashers run 50% more quietly than 10-year old models.

Help the Environment:
Less energy means less pollution and greenhouse gases in the environment. Less water consumption helps protect our lakes, streams and oceans.
Stay away from the heat-dry, rinse-hold and pre-rinse features and try the air-dry option instead.

You can read more here about choosing a Frigidaire dishwasher.