Dishwasher Electricity And Water Use

Having purchased two dishwashers over the years we thought it would be worth sharing some of the selection criteria we used.

Dishwasher Water Use

A survey of the published water use for a range of machines from the cheap to the very expensive demonstrated a wide range of between 20 and 12 litres per wash. The published figure is however somewhat misleading in that this is under optimal conditions and the machine we chose (after careful reading of the manual) showed it could actually use between 12 and 17 litres per wash for a 12 litre machine. Checking into the cheaper machines gave similar results. Whether you can use the most economical program or not it still seems that the more expensive machines give lower water consumption. On the positive side it looks like one load is the equivalent of two 8 litre bowls of water giving a net saving of 4 litres on the most economical setting for the machine we purchased.

Dishwasher Electricity Use

The electricity consumption during use seems pretty consistent irrespective of the price of the machine with a typical figure of 1.6KW Hr per wash for the most economical complete wash cycle. It has been impossible to establish the standby power from the literature or by questioning staff and in one case contacting the manufacturer where machines have a timer facility rather than an on/off switch. The machines we chose had a real on/off switch plus the facility to leave it on standby to come on a number of hours into the future (probably the best compromise). The actual standby current was measured as 1 Watt on both machines. On the positive side we saved 1 to 2KW Hr per day on the water heating which was electric in our first house.

Dishwasher Running Costs

Using the figures for water use above a cheap machine will cost between £13 and £35 extra to run daily over a period of 5 years and a more expensive machine will vary between a saving of £13 and and a cost of £3 extra if used daily over a period of 5 years. These figures for water use are compared to doing it all by hand.

Using the figures for electricity use above the costs will be about £15 per quarter for a cheap machine with no timer and about £6 per quarter for a more expensive machine with a timer that can be used on cheap rate electricity. One way of reducing the electricity cost of a machine with no timer is to fit a time switch so cheap rate electricity can be used.

So it is worth paying a little bit more for the machine to use less water for about the same total cost over a 5 year period - this is the decision we made. The original predicted saving of £2 per year for water and no cost change for electricity made when the first machine was purchased now looks pessimistic since we are only using the machine approximately twice every five days.