The household water heater should be set no lower than 130 degrees. Any lower can cause bacteria to grow in water tank and then circulated to the whole house. The temperature of the water coming out of the kitchen sink should be around 120 degrees. The water inside the dishwasher will be higher, to about 140 degrees. Most dishwashers have a heating element that heats the water to a higher level.
If the water is too cold inside the dishwasher, the dishes will not get as clean as they should be. This will result in having to wash the dishes again. This is waste water and electricity. Set the temperature of the water heater near 130.