The t-stat will throw a OBDII troble code, which can be read by an OBDII code reader or OBDII scan tool.
The water pump thows trouble manufacturer-specific (i.e. BMW) trouble codes that can only be read by a BMW-specific scan tool such a Bavarian Techniques unit. It looks like you are scanning the car with an OBDII tool, which is why you are not finding the trouble codes for the water pump. Get the car scanned with a BMW scan tool.
There is a thread in the maitenance section started by ENINTY that has all of the detailed inforomation about how the water pump fails. Search for that thread and it will tell you all you need to know.