The answer to 'why is my bathtub rusty water' is that the rusty water is likely caused by iron or mineral buildup in your plumbing system. This can happen over time as the metal pipes and fittings corrode, releasing rust and discoloring the water.
Some common symptoms of rusty water include reddish-brown stains in the bathtub, sink, or toilet, and a metallic taste or odor to the water. This can be a nuisance, but it's generally not a serious health hazard.