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Which? research reveals how little water dishwashers use compared to hand-washing

Our tests show even the least water-efficient dishwasher still only uses half the amount of water compared to hand-washing
Washing up dishes

Our in-depth testing has found that dishwashers are, on average, four times more water efficient than washing by hand per place setting.

The most water-efficient full-size dishwasher uses almost 10 times less water to wash the same amount of dishes as washing them by hand.

Plate for plate and glass for glass, full-size dishwashers are more efficient than their slimline counterparts. This is because you can wash more dishes in them with only a little bit more water used.

However, even if you were to use the most thirsty slimline model available, it would still use half the water that hand washing does.

Graphic showing full size, slimline and hand-washi

Shopping for a new dishwasher? We've recently found some that match fantastic energy and water-efficiency with brilliant cleaning and drying. Read our dishwasher reviews to find out which is best.

What our dishwasher testing shows

When washing up, we estimate that you can wash around two standard meal sets with one washing-up bowl (average capacity of nine litres) before you'd need to empty the water and fill it again.

One standard meal set is equivalent to one place setting in a dishwasher: one dinner plate, dessert plate, soup plate, glass, saucer, cup and set of cutlery.

However, dishwashers don't just wash one or two place settings at a time; some can wash up to 16 in one wash. To make it an even comparison, we filled a dishwasher up to the max before putting it on.

We then divided the water used in one wash by enough to just wash two place settings - one washing-up bowl. Doing this, we can get an even comparison.

We found that all dishwashers, even the least water-efficient, can wash twice as many dishes using the same water.

  • 19 sets - Best dishwasher
  • 9 sets - Average full-size
  • 7 sets - Average slimline
  • 4 sets - Worst dishwasher
  • 2 sets - Hand Washing

This is based on all the dishwashers we've tested in the past eight years (423 full-size models, 133 slimline models, in total).

What about energy use?

Dishwashers on average use about 1.10kWh of energy per wash. This costs roughly 20p, based on 18.75p per kWh, although that will of course depend on your energy provider.

How much energy used to heat up water for your washing up bowl will depend on the heater.

We calculate energy running costs for dishwashers. The most efficient costs almost half as much to run, compared to the priciest.

If you have a gas-heated water tank, it isn't an easy comparison (a bit like apples and pears). Gas is typically cheaper than electricity, but is worse for the environment.

According to analysis by clear-heater.co.uk, an average electric immersion heater costs about 44p to heat up enough water for an 80 litre bath.

That means a nine litre washing up bowl will cost roughly 5p to heat up. As dishwashers are able to wash more in a single wash, using less water (and hence having less to heat up), they could be more energy-efficient, too.

Want to know more? Read our guide to dishwasher energy running costs to find the most efficient dishwasher for your home.