How many times have you heard that using a dishwasher is more energy or water efficient than hand washing your dishes? Pretty much every time you have purchased a dishwasher?

But what is the reality behind these claims? What actual facts can you take into account next time you need to make a similar decision to buy, or not to buy a dishwasher?

Some quick research into the ‘dishwashing is more efficient’ adage, checking out several manufacturers’ claims, showed the data used in the cases studied tracked back to the same German study.

However, review of the original research shows the comparison undertaken with handwashing as the base case showed that the majority of European people in the study washed their dishes and then rinsed them under continuously running hot water. For the entire duration of the time they were washing dishes, they had the hot tap running so they could rinse them.

This may be a cultural quirk or it may be one of those ‘selective study’ things designed to achieve a certain outcome, but this certainly does not seem to be the norm among those who hand wash their dishes. If you know of people who run the hot tap continuously, or if this is common behaviour in Europe or elsewhere, please mention as much in the comments.

According to the study, average water use of the typical hand washer used between 130 and 447 litres for a single wash of a 12-place setting. There was a  ‘minor’ group in the study who were what they termed ‘water economisers’ but who still used 30 to 100 litres per wash. This is the baseline that is used to make the claims about how much more energy and water efficient dishwasher are than handwashing. In my mind, this is a highly spurious base case.

In a water-conscious country like Australia, it is highly questionable whether most people would use any thing like that amount. In Queensland, for instance, the average post-drought water consumption per person has now rebounded from the post-drought low of 147 litres per day to approximately 170 litres per day. That figure, however, includes showering, pools and garden watering!

The average 20-litre sink (when filled so it will not splash out) contains around 15 litres of water, about the same amount of water used by an economiser dishwasher. If you rinse in a second sink half full, then that means you are using 10 litres per wash more than a highly efficient dishwasher on an economy cycle. So depending on your personal practices, the size of the wash, the number of sink water changes, the amount of food still attached to the plates and so on, the question of what is more efficient water wise, will change.

In considering the energy used to heat the water, a single bowl of suitably hot (warm) water uses less than 1kW of energy while dishwashers use between 1kWh (standard cycle) to 2kWh (intensive cycle) of electrical energy per cycle no matter how many items are in them.

So when considering hand washing vs dishwashing, the upshot is:

• if you wash in one or more sinks full of water at breakfast and dinner, dishwashers are more efficient energy and water wise, provided the dishwasher is only used once per day and is full when operated
• if you hand wash in one sink of water per day, the water consumption is the same as a highly efficient dishwasher cycle and twice as energy efficient as the dishwasher, provided also the dishwasher is only used once per day
• using the dishwasher twice per day, compared to hand washing in two sinks twice per day uses double the amount of water, and the same energy for the standard cycle and half the energy of the intensive cycle
• using ‘drawer’ type dishwashers is more efficient than large dishwashers if you have small loads or require more frequent loads
• hand washing is likely overall to be the most efficient solution for small households with one or two people if they conserve water when washing and do not rinse in running water.

None of the above takes into account the additional embodied resource and pollution impacts of the life cycle of dishwasher manufacture, maintenance or end of life and resource impacts. Nor does it take into account the additional and more environmentally aggressive chemicals used in automatic dishwashing compared to hand washing or that no Australian manufacturers (to my knowledge) have engaged the same extended producer responsibility (EPR) or Product Stewardship schemes that they are legally required to undertake in Europe. While the resource capture potential is inherent in many of the products, in Australia it is largely under utilized.

If any manufacturers have better, more accurate or more socially relevant data, feel free to leave a comment below.