During a recent kitchen run-in with a fellow brown-bag luncher, he asked whether washing dishes by hand is more or less efficient than using a dishwasher. After a little research, it looks like unless you are able to wash and rinse a dish with less than 4.4 seconds of running water, the dishwasher will always come out on top.

Researchers at the University of Bonn conducted a test comparing the energy consumption and performance of manual dishwashing with that of dishwashing machines. Water and energy consumption was compared for 113 people from 7 countries for the amount required to wash the equivalent of 12 place settings of dishes (the average dishes washed on a daily basis in a typical home). The results were pretty astounding – the average test subject used 27 gallons of water and the equivalent of 2.5 kWh of water-heating energy (not to mention around 80 minutes of manpower). The dishwashing machine on the other hand, cleaned the same amount of dishes using half as much energy and 1/6 as much water!

There are a few caveats to the dishwasher’s cleaning domination – it obviously doesn’t discriminate on water or energy usage based on how full it is, so fill ‘er up before hitting start. The energy efficiency of the dishwasher is also a factor – choose EnergyStar or other highly efficient appliances.

A few other tips for becoming a greener dishwasher:

  • remove large food scraps with a fork or spoon before placing dishes in the dishwasher
  • if washing by hand, do so right after a meal – it is easier to wash dishes if food is not dried on the dish
  • whether washing by hand or using a dishwasher – don’t pre-rinse the dishes
  • manual dishwashing is most efficient with a two-bowl sink – one for hot, soapy water to wash and one with cold water for rinsing
  • don’t use too much or too little detergent
  • use the internal heater in the dishwasher. Many dishwashers made since the early 1990s have an internal heater to boost the water temperature to the optimum dishwashing temperature of 140F. You can lower the temperature of your household water heater to about 120F.
  • choose to air dry whenever possible. By turning the heat dry setting off, you will conserve the energy it takes to dry your dishes. Instead, open up the door at the end of the cleaning cycle and let them air dry.
  • try out a homemade detergent like this one – add 1 tablespoon of Arm & Hammer Super Washing Soda and 1 tablespoon of 20 Mule Team Borax to your detergent dispenser and distilled white vinegar instead of the clear rinse gel.