An electric tank water heater is two large elements (often about 4,500 watts each) that take turns recovering the tank. You do not pay 4,500 watts all day. You pay recovery after showers, laundry, and dishes, plus standing loss as the tank slowly cools.
A heat-pump water heater is a different machine in Whatt (its own card) and usually uses far fewer kWh for the same hot water. Tankless electric still has a high wattage while someone is drawing hot water; the minutes are just shorter.
The water volume is a water-card problem. The electricity to heat that volume is this card. A long hot shower shows up on both sides of the house if the heater is electric.
Set hours of recovery or a typical daily kWh habit if you know it from a monitor. Standing-loss-only days still have some runtime.
At 18.8¢ per kWh, one hour of a 4,500-watt element is 4.5 kWh — about 0.85. Two recoveries like that in a day is about 1.70 of usage, before other appliances. That is why “take shorter showers” is also an electric tip in all-electric homes.
How the shower is heated
Gallons are the shower card. This card is the electricity to reheat the tank. If the heater is gas, this electric-tank story is the wrong machine — pick the heat kind on the water fixture instead.
Related
Usage estimate only — not a utility bill, load calc, or advice.