Once only found in the kitchens of the wealthy, dishwashers have had a steady growth since they were first introduced to the UK in the 1950s, with nearly 50% of homes having one at the last count in 2018.
However what was once a kitchen workhorse is now standing unused in many homes as families return to washing up by hand, assuming it is a cheaper way to deal with dirty pots during the cost of living crisis. While there's no doubt a dishwasher saves water, whether it saves energy is not so straightforward.
Looking at water use first, you would have to be amazingly mean with water to use as little to hand wash your dishes as a machine does. Recent research by consumer group Which? showed that even the least water-efficient dishwasher still only uses half the amount of water compared to washing by hand, and the most water-efficient full-sized dishwasher uses almost 10 times less water to wash the same amount of dishes as hand washing them.
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To carry out the test, Which? used the equivalent of the one place setting standard used by dishwasher manufacturers, which is one dinner plate, dessert plate, soup bowl, glass, saucer, cup and set of cutlery.
When washing up, Which? estimated that you can wash around two standard meal sets with one washing-up bowl (average capacity of nine litres) before you would need to empty the water and fill it again. Even the worst performing dishwasher only used 4.2 litres of water for the same size place setting and the best performing used a meagre one litre for two settings.
Of course, it's more economical to use a dishwasher with a full load, so the figures were derived by dividing the water used in one full wash by enough to just wash two place settings - one washing-up bowl. Doing this, there is an even comparison. The figures showed that all dishwashers, even the least water-efficient, can wash twice as many dishes using the same water.
So what about energy usage? This is when things get a little more complicated. Most dishwashers are cold-fill only and heat the water they use by electricity, on average about 1.12kWh of energy per wash. Based on the new energy price guarantee average of 34p, it will cost around 38p to get your dishes clean.
So far, so simple. The complication comes when Which? tried to make a comparison between hand-washing and dishwasher use to see which used the least energy, as how much energy it takes to wash up will depend on how you heat the water you use. If you have a gas-heated water tank or a combi boiler, this isn't an easy comparison to make, as gas is a lot cheaper than electricity at 10.3p per kwh under the energy price guarantee, but it depends on how efficient your heater is to how much gas you use.
Electricity is more straightforward and if that's how you heat your water, a dishwasher is probably the cheapest to wash your dishes. If you use an electric immersion heater that's 3kW, it will cost roughly 16p to heat up a nine-litre washing up bowl, which would be enough to wash up two place settings. With a dishwasher coming on average 38p for a load that generally holds 12 place settings, you could use around 96p to wash up the same amount by hand.
But while there's no absolute answer whether hand-washing your dishes or using a dishwasher is more energy-efficient, there's plenty you can do to make sure you're using less energy whichever way you choose to do the dishes, according to Uswitch.
If you use a dishwasher:
1. Use the economy or eco programme
Every modern dishwasher has a special energy-efficiency setting that can save up to 20% of energy by using less power to heat the water. Eco programs wash dishes at lower temperatures and with less water, but for longer to still ensure a thorough clean. On average, economy programs use 30% less energy and water compared with the main program.
2. Wait until your dishwasher is full before putting it on.
Washing a half load of dishes simply wastes half the energy produced by your dishwasher. Aim for a full load each time, but be careful not to overfill the dishwasher. Make sure water from the spray arms can reach every item, if not some won't get cleaned properly. Large items should go at the back and sides of the racks, too. If big plates are at the front, they can stop the water from reaching the detergent dispenser.
3. Don't pre-wash.
It isn't necessary and wastes water. Just scrape food into the bin.
If you wash up by hand:
1. Always pre-soak
Heavily soiled or greasy dishes should be soaked in a bowl, rather than rinsing them under the tap before you start your washing-up.
2. Always wash your dishes in a bowl
Don't wash your dishes under a running tap. A bowl will keep the warm water together without requiring you to constantly waste hot water.
3. Use a second bowl for rinsing
Don't rinse dishes under a running tap. This is another easy way to save both water and energy for heating.
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