Several things could make your hot water run out quicker than you expect, such as: Your family is growing: When you have more people using hot water, or more people taking longer showers, hot water won't stay in the tank for too long High demand for hot water at once: Performing multiple activities that need hot water simultaneously, such as running the dishwasher while someone is showering, could drain your hot water tank quickly Incorrect temperature setting: Your water heater could be at the wrong setting and hence, not producing hot water at your desired temperature Defective heating element: When your lower heating element goes bad, there'll be a significant drop in the amount of hot water produced