Several things can cause your home's hot water supply to run out faster than normal. The most common culprits are sediment buildup, a faulty lower heating element, and a broken dip tube. Sediment buildup occurs when a layer of dissolved minerals settles at the bottom of your hot water storage tank. The buildup can grow big enough to displace a significant amount of water in your tank. If the lower heating element of your electric water heater suddenly goes bad, you'll notice a significant decrease in the amount of hot water right away. When a dip tube gets damaged, cold and hot water mix in the tank, lowering the overall temperature of water you get.