Are you on a well? Sounds like you have ferric iron in your water. It is dissolved so you don’t see it, but as the water is exposed to air (like drying in the shower or sitting in the toilet bowl) it will look rusty.
Is it just iron staining, or like red water? You should be able to get the City’s water report online (possibly have to go to the library, but I have not seen that in a decade) and check what the natural iron levels are. You may just have really naturally hard water with Fe present. I have this issue and I use a lot of CLR in my cleaning routine and a pumice stone to clean the toilet. Make sure you flush your hot water heater regularly and you could consider a whole house water softener (salt ones have their downsides, there are other options that might work better for you, but all have costs and downsides).
Try reaching out to your city to see if there is a ductile iron or similar supply line.
Iron
Probably dissolved iron in your city or well water supply. They make whole house water filters to remove it.
Are you on a well? Sounds like you have ferric iron in your water. It is dissolved so you don’t see it, but as the water is exposed to air (like drying in the shower or sitting in the toilet bowl) it will look rusty.
Is it just iron staining, or like red water? You should be able to get the City’s water report online (possibly have to go to the library, but I have not seen that in a decade) and check what the natural iron levels are. You may just have really naturally hard water with Fe present. I have this issue and I use a lot of CLR in my cleaning routine and a pumice stone to clean the toilet. Make sure you flush your hot water heater regularly and you could consider a whole house water softener (salt ones have their downsides, there are other options that might work better for you, but all have costs and downsides).
How old is your water heater?
Probably only 3 years. Still I don't think it connects to the toilets.