HERE'S a great argument for buying a dishwasher. Contrary to popular belief, the machines use less water and electricity than people do when they wash dishes by hand. "Common sense is wrong," says Gereon Broil of the University of Bonn in Germany, who was a member of a team that surveyed the dishwashing habits of 75 people and compared their performance with that of a typical modern dishwasher. People used on average six times as much water as the machine to clean the same number of dishes, and heating the water consumed more than twice as much electricity. Rinsing plates under running water was particularly wasteful. One volunteer sent a staggering 345 litres of water down the drain when a dishwasher would have used only 15 litres.