The time it takes for an electric water heater to heat water depends on the size of the tank and the initial temperature of the water. On average, it can take anywhere from 1 to 2 hours to fully heat a 40-gallon tank of water. This is slower compared to gas water heaters, which can heat the same amount of water in about half the time. If you have a high hot water demand, this slower recovery time might be noticeable, especially if multiple appliances or showers are using hot water simultaneously.