The carbon footprint of doing the dishes:
Almost zero CO2e: by hand in cold water (but the plates aren't clean)
540g CO2e: by hand, using water sparingly and not too hot
770g CO2e: in a dishwasher at 55°C
990g CO2e: in a dishwasher at 65°C
8000g CO2e: by hand, with extravagant use of water
When it comes to long-standing green-living debates, washing up by hand versus using a dishwasher is right up there with hand-driers versus paper towels. So here, finally, are some carbon-footprint figures, which hopefully will put the issue to bed for once and for all.
As the numbers above show, the most careful hot-water handwashing just about beats a fully loaded dishwasher. This is partly because most people (in the UK at least) do their manual washing up using hot water heated by a gas-fired boiler, whereas dishwashers heat water from cold using electricity. A modern boiler can capture more than 90% of the energy in the gas, whereas most of the energy in the fuel used to generate electricity is wasted in generation and transmission, which gives handwashing an obvious head start.
However, according to plenty of anecdotal evidence and at least one study, few people are really careful with hot water when washing up. If instead you leave the hot tap running – as many people do – then the footprint is far higher than using a dishwasher. And even if you do wash up carefully by hand, compared with the dishwasher you still lose out both on hygiene (with nearly 400 times more bacteria left on the dishes after washing) and time (taking nearly four times as long as loading the dishwasher).
Overall, then, it's probably fair to say that the dishwasher wins – assuming that you use appropriate cycles and only run the machine when it's full. This is true even if you include (as the figures above do) the energy used in the production of the dishwasher in the first place. The footprint of an appliance's manufacture is impossible to pin down accurately, but a reasonable estimate would be 130g of CO2e per cycle for a fairly expensive "built-to-last" model that you keep for 10 years.
As for water consumption and detergent, these aren't included in the numbers given above because they're negligible compared with the impact of heating the water in the first place.
The conclusion, then, is get a dishwasher if you want one. Or, if you have one already, don't feel guilty about using it. To maximise the benefits, always choose a model that will last and then look after it. Try to run it fully loaded, use the economy setting when possible and – for maximum green points – use the timer setting to run the dishwasher in the middle of the night. This way, you'll be using the grid at a time of low demand, which means the least efficient and dirtiest power stations won't be running and, as a result, each unit of power will have a slightly lower carbon footprint.
• This article draws on text from How Bad Are Bananas? The Carbon Footprint of Everything by Mike Berners-Lee
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