Recently on a start up I noticed an unusual whining noise from the engine area, sounded like it was coming from one of the pulleys.  The first thing that came in my mind was the idler or tensioner pulley probably went bad.  So I removed the air box assembly and the belt to check each individual pulley for noise.  A simple way to check for a defective pulley is to grab the pulley and see if you can get it to wiggle, if it wiggles most likely the bearings are shot.  When I got to the water pump pulley it was wiggling and also making grinding noise when I turned it.  Upon close investigation I noticed that it was also leaking coolant from the bearing area.

The part number for a new water pump is: 996 106 011 53, the gasket is 996 106 340 51 total cost for these replacement parts were about $300.
You should also have couple gallons of coolant handy as during the replacement process you will loose quit a bit of coolant.

The only two special tools needed were for coolant hoses (A tool that allows you to spread the clamp on the coolant hose, and a hose clamp which allows you to clamp the hose shut). 

I only had to jack the car up about 6 inches off the ground to have enough clearance to gain access to all the components. 

Remove the air box and the belt, please refer to the SAI valve replacement DIY for the procedures

Place a floor jack under the engine jack point (the retangular block right in front of the engine pan) and lift the jack so that the jack touches and slightly unloads the engine from the engine mount.

Please a receiver pan under the engine directly below the coolant drain plug.  Unbolt the drain plug and let the coolant flow out and then install new washer for the drain plug and reinstall drain plug and torque to: 7.5 -11 ft lb.

I clamped the small coolant hose connected to the water pump from above at the engine bay.  I used a latex glove to cover up the end of the large coolant hose once I disconnected it from the engine and used a zip tie to held the latex glove in place.

Unbolt the two 13 mm bolt for the Catalytic converter bracket on each side of the catalytic converter and slide it on to the side.

Unbolt two 13 mm bolt on the catalytic converter bracket that secures it to the engine carrier bracket, remove bracket

Unbolt two 15 mm, one 10 mm bolt on the engine carrier bracket from the underside of the engine, completely remove the bolt

Loosen (not completely remove, back the bolt out to the end of the thread) one 15 mm bolt on the left side of the engine carrier bracket, can be reached from the bottom of the engine using a 15 mm wrench

Loosen (not completely remove, back the bolt out to the end of the thread) one 15 mm bolt on the right side of the engine carrier bracket, can be reached from the tom of the engine area using a 15 mm socket and ratchet.

Slide the engine carrier bracket away from the water pump.

 

There are a total of seven 10 mm bolts that holds the water pump in place.  Be careful to note the position of each bolt once you have removed them as one of the bolts is longer than the rest.  All the bolts comes off fairly easy with a 1/4 ratchet with the exception of one bolt on the right side of the water pump right next to the engine block.  But I had no problem removing that bolt using a long 10 mm socket on a 1/4 ratchet.  Once that bolt is loosen you can turn the bolt out using just the socket and your finger.

After the old water pump is removed you will need to cut the old gasket off from the engine by snipping the old gasket at the connecting web. 

Line up the new gasket with the new pump and cut off the unused portion at the connection web.

Install the new water pump with gasket as one unit.

Install coolant hose.

Install belt and air box housing.

Fill the reservoir with new coolant 50% + 50% distilled water mix.

Start the car and park it on a incline front facing down.  Let the engine run and cool off, check reservoir level for additional coolant.

Additional information contributed by Joost Perquin in October, 2008