Water Heater is the second largest contributor to the energy bill after the air conditioner/central heat. Water has high heat capacity, so it takes a lot of energy to warm up. For example, it takes one kilowatt-hour to warm up about 10 gallons of water from 80F to 120F. Your electric or gas bill is noticeably affected by how much hot water you use in your house. That includes showering, clothes washer, dishwasher. Here are some general guidelines for how you can reduce your water heater energy use:

Washing Dishes

• Set water heater’s temperature at no higher than 120F, especially if you don‘t have a temperature sensor on your dishwasher or clothes washer. Here is why, it takes 1 kilowatt-hour to heat up 10 gallons of water from 80F to 120F. If your water heater’s thermostat is set at 140F, it will take 1.46 kilowatt-hour to heat up the same 10 gallons of water. That is almost one and half times more energy for the same amount of water. If your dishwasher does not have a temperature sensor, it will use the same amount of water from your water heater, whether its temperature is 120F or 140F. Most dishwashers have a minimum water temperature requirement of 120F, so any temperature above 120F would not make a difference in cleanliness of dishes.
• If you have to rinse your dishes before you put them into the dishwasher, rinse them with cold  water. Cold water does not require energy input.
• If you don’t like the idea of rinsing dishes with cold water, rinse them with warm water but don’t open the faucet all the way.  Open it just enough to get some flow and it will be just as effective as having the faucet fully open.  It will significantly reduce your hot water use.  Here is a test you can do.  All you need is a bucket of known volume (they usually come in 3- or 5-gallon sizes) and a stop watch.  Place the empty bucket in your kitchen sink, turn on the faucet at the same flow you usually rinse or wash your dishes and use a stopwatch to time how long it takes to fill up the bucket.  Then do the same experiment with using the low flow.  Here is what I got from my test:

1. The first time it took me just under 1 minute to fill up at 3-gallon bucket, Assuming that it takes you 10 minutes to rinse/wash your dishes, with the average water temperature of 100F, you will use up 30 gallons (3 gal * 10 min = 30 gal) of water at 100F. It will take 1.46 kilowatt-hours total to rinse your dishes (assuming your cold water is 80F, if it is lower, it would take more energy).
2. When I timed my low flow conditions, it took me 8 minutes to fill up the same bucket. This time my flow was 3gal/8min = 3/8 gallons per minute. For 10 minutes I would use 30/8 = 3.75 gallons total. It would only take me 0.183 kilowatt-hours to wash my dishes. That is (1.46/0.183= 7.98) almost 8 times less energy use!

To find out how much energy your dishwasher uses, see my post Find Energy Use by Appliance. Dishwashers use between 4 and 6 gallons of water per cycle.  Energy Star dishwashers use 4 gallons and non-Energy Star use 6 gallons.

Showering

Average flow from the shower head is 2.5 gallons per minute.  So if you are taking a 10-minute shower, you are using 25 gallons of warm water.  It takes 1.3 kilowatt-hours to heat up this much water from 80F to 100F and double that if the cold water temperature is 60F.

• Now days market is flooded with all kinds of low-flow shower heads.  My shower head has a lever that adjusts the water flow by adjusting the size of the holes for the water to flow through. Low-flow shower heads use up to half of the flow of regular shower.
• Another no-brainer is to take shorter showers!

Washing Laundry
Average clothes washer uses 40 gallons of water per cycle.  Your energy use will depend on the cycle’s water temperature.  The hotter the temperature, the more energy it will use.  So here are some tips:

• Choose a cycle with cold rinse, rather than warm or hot rinse.  It is not the “washing” part that takes a lot of water, it is the “rinsing” part.  So washing in hot or warm water won’t consume nearly as much energy as rinsing in hot or warm water.
• The operation of washer itself does not consume a lot of energy.  You can find out how much power your washer uses by checking out Find Energy Use by Appliance.

As a general guideline for the water heater, if you are leaving town for few days, it is good to turn off the water heater as well.  This way it will not use the energy to maintain the set temperature.  In the perfect system, all of the heat would stay within boundaries of the heater.  This is not the case in the real world, some of the heat does escape to the surroundings.  If you go and touch your water heater, more likely it is going to be warm (if it is on).  This is the heat escaping to the surroundings.