How Much Water Does Dishwashers Use?

To help the environment and save water, people are now taking effective steps and one such step is getting the dishwashers installed. People often question how much water does a dishwasher use and which method is water-efficient, hand washing or using dishwashers. A study states that using dishwashers is way effective as it uses half the energy, less soap and 1/6th of water for washing in comparison to hand washing. However, there are several factors which might affect the comparison results like frequency of doing the dishes, hand washing habits of people and the way water is heated.

dishwasher info-graphics

Water efficiency dishwasher’s comparison

Built-in Dishwashers vs. Hand Washing

Built-in dishwasher efficiency

A normal dishwasher makes use of 6 gallons in comparison to an energy star rated appliance that uses 4 gallons per cycle. The usage of energy ranges from 1.59 kWh – 0.87 kWh per load.  If you look at the CO2 emission numbers of Department of Energy, it is 1.34 pounds of CO2 Emmons at per kWh. This calculates that with every 4 gallons of water, 1.16 – 2.13 lbs of CO2 is emitted per load.

According to Energy Star, a standard certified dishwasher which is 24 inches has an equal capacity or more than six serving pieces and eight place settings. So, here we will be considering the same amount for how many dishes will be washed using hands.

Use Dishwasher

Hand washing efficiency

If you are looking for the answer that is hand washing better than using a dishwasher then the shortest answer is maybe. First, look at water usage.  2 gallons of water flows out from an average kitchen faucet, so it is a pretty simple calculation that if you are taking more than 2 minutes then you will be using more than 4 gallons of water. This is enough to state that you should be using a standard dishwasher instead. To be more precise, let’s assume that you are washing 48 pieces of dishware, 6 pieces per setting and 6 serving dishes. This makes a total of 54 pieces of dishware which you have washed in 4.4 seconds and 9.5 ounces of water for each dish.

hand wash

Impacts of heating the water

Let us that you use lukewarm water for doing the dishes. The water is a mix of half hot and half cold. To heat 2 gallons of water with gas water heater of your house will take 960 BTUs or you can say about 0.9% of one therm with the assumption of 100% efficiency of the heater. In this, we have also assumed that water entered your house at 60 degrees which will be heated up to 120 degrees.

Heating Element

Tank water heaters

The efficiency of a gas water heater is more than any other kind of water heater. It is 65% more efficient and takes 1477 BTUs to heat water or 1.5% of a therm. According to the US Environmental Protection Agency, 11.7 pounds of CO2 is emitted from the usage of one therm so that makes 0.17 pounds of CO2 being emitted by heating 2 gallons of water.

However, if you are using a tankless water heater then it would change the numbers because they are approximately 80% efficient. They work on a bit lower scale i.e. 1200 BTUs which will emit 0.14 lbs of CO2, approximately. 

If you look at electric water heaters they are different than gas heaters. Electric water heaters are less efficient as they use 86% – 93% of energy for heating which is 60-65% in gas heaters. It will take 960 BTUs or 0.28 kWh to heat 2 gallons of water with its 100% efficiency. According to EPA, 1.715 pounds of CO2 is emitted from 1 kWh, thereby heating 2 gallons of water will emit 0.51 pounds of CO2.   

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