Fill two pots about the same size with the same amount of water. Start the heat on both at the same time, with the heat at the same level. See which one boils first. It should be the covered pot. Imagine how much energy we can save if everyone covered their pots when they cook.
Washing dishes takes hot water and it takes extra energy to heat water.
If you have a dishwasher, you're using electricity too. If you leave the water running while you're washing dishes, gallons of water go down the drain unused. If you could save all that hot water, you would have enough for a hot shower. You could reduce the amount of water you use by up to 50 percent. Scraping off the food may be enough.