Photograph by Philippe Bourseiller
When you wash the dishes by hand, fill the sink or washing-up bowl, rather than washing each plate under a running tap. Hand-washing dishes typically uses about 63 litres per session. Better yet, invest in a water-efficient dishwasher - if you use a machine wisely, it can use as little as 10 litres of water, much less than even careful hand-washing practices.
-from the book '365 Ways to Save the Earth' by Philippe Bourseiller
Personal Note: To be honest, I find this one to be a toughie. I can't get myself to rinse dishes in a water filled sink. I try to turn on the tap at a lesser flow instead.