I have always, and I'm sure most people at home do, filled the dishwasher up completely before turning it on. That's quite a substantial load of dishes each tim

I have always, and I'm sure most people at home do, filled the dishwasher up completely before turning it on. That's quite a substantial load of dishes each time, 2 meals worth + sundry in a 5 person household. The dishwasher I have says it uses 6 litres per wash on the normal automatic mode. That's just over 1.5 gallons, and even if a total lie and it uses twice as much that's still only 12 litres / 3 gallons. Where it probably falls down is where they have dishwashers in office kitchens where they don't fill it up and chuck it on anyway so they have their favourite coffee mug ready for the morning.