2000 BMW 528 radiator repaired then water pump breaks why?

Depending on your milage, with the 1995-2003 528i BMWs, it's recommended that the entire cooling system be replaced when it's time to replace one of the big elements such as the Radiator, Water Pump or Thermostat. The reason for this is: 1. It saves time because all of the parts are in the same area & 2. These components usually fail within 10k-20k miles of each other. When you get your Water Pump replaced, you might want to look into replacing the Serpentine Belts, Belt Tensioners & Rollers and the Thermostat.