Washing dishes by hand usually uses more water especially if you're leaving the water running while washing and rinsing the dishes.
When you load your dishwasher up fully and then turn it on the dishwasher will actually use less water to wash the same amount of dishes and it saves you time and work as well.
You can load the dishwasher up with dishes and then go do something else more productive or fun while the dishes are being washed by the dishwasher.
I used to wash dishes by hand and I find that using the dishwasher is much faster, easier and cheaper than washing the dishes by hand.
Good energy efficient dishwashers use less energy and water than washing the same amount of dishes by hand.