If its rusty coloured water only,
can we asume you havnt been running a proper mix of anti freeze/summer coolant which works as a rust inhibitor.
If everything is running fine just now & temp is good.
close the heater controls, drain & flush the coolant system well.
Fill not too full with the correct antifreeze mix for your vehicle, bleed as your engine type requires,
do a test run, & after the system has cooled, top up the system not over filling.
If at anypoint in the past 'rad weld' or similar was put in, you will probably find a leak quite soon after putting in the antifreeze.
Just a case of tightening hoses, clips or getting the gasket or radiator sorted out,
no panic.
(save your new coolant mix while doing this)
Best time of year to get it done, autumns nearly here.
have fun.
george
