The answer to 'why is my water heater rusty water' is that a rusty water heater is typically caused by corrosion inside the tank. This can happen over time as the metal components of the water heater break down, allowing rust and sediment to accumulate in the water. Rusty water can also be a sign of a more serious problem, such as a leaking tank or a failing anode rod.
If you're seeing rusty water coming from your water heater, it's important to address the issue right away. Leaving a rusty water heater unattended can lead to further damage and even a complete tank failure, which can be expensive to repair or replace. In some cases, you may be able to fix the problem yourself, but it's often best to call in a professional plumber to diagnose and address the issue.