My car has had a new water pump and thermostat housing unit but still loosing water daily, why?

SOURCE: I am loosing coolant and

If you are not seeing fluid spots on the ground chances are you have an head gasket problem

SOURCE: OVER HEATING

In the fan circuit...You have a temp switch screwed on the radiator, a fuze and a relay in the fuze box plus a fan.  Swap the relay with another relay, replace the fuze.  The other fan should come on when the a/c is turned on.  If you fix the fans and it still overheats, you may have a BLOWN HEAD GASKET.  ALSO ARE YOU BLEEDING THE AIR FROM THE SYSTEM?  DO YOU SMELL EXHAUST IN THE COOLANT?   

SOURCE: car is still overheating after new thermostat, new housing.....

bleed air out cooling system. put half antifreeze and half water .if you got too much water .it willl cause engine to over heat. antifreeze raise boiling point .220 degrees it wont boil away . water will evaporate 212 degrees.it will boil away .causing low coolant problems and over heating.

SOURCE: Leaking water from top of water tank

rad caps are common for trouble, bottom of rads leak and a pipe that clicks into the rad leaks.
there is a core plug at back of engine that leaks, gearbox and fly wheel has to come out.
why dont you add a dye so you can see where it has come out. have pressure tested it to 25 psi and left to see where leaking,

SOURCE: coolant leak and overheating

I had a water leak on my 730i I found it after much trouble.A hairline crack in the plastic thermostat housing which onlly opened up when hot and of course got worse as water level dropped.Hope this helps.