The answer to 'shower rusty water' is that the most common cause is corroded pipes or water heater components. Rusty water can be a sign of iron or mineral buildup in the plumbing system, which can lead to discolored, smelly, or even contaminated water.
Some other common causes include old galvanized steel pipes, high iron content in the municipal water supply, or a malfunctioning water heater. If the rusty water is only coming from the shower, it may be isolated to that fixture or pipe, rather than the entire home's plumbing.