coolant leak

[we350z]

Hi - been a while since I posted here but it looks like my 200 X5 4.4i has developed a coolant leak somewhere. It has almost 74,000 miles now. I first noticed a small amount of condensation under the front of the vehicle (from the middle of the skid plate/center jack point area) when I drove the vehicle back from Lake Tahoe to San Francisco about a month ago. I think the car probably sat for about two weeks before the next time I drove it and I didn't see anything on the ground but I started smelling some coolant. Then I drove the car a week later and the "Check Coolant Level" check control light came on. I checked the reservoir and it was empty/low so I filled it up with distilled water. This worked fine but then the same thing happened today. I filled it up again and then I noticed after the trip to Oakland and letting the car sit in the parking garage for about 4 hours a small greenish puddle had accumulated under the car. It looks like its coming from above the passenger side of the skid plate but could have just been the angle the car was sitting on the on the parking garage floor. I checked the reservoir and I don't notice any fluid around there (I believe this was previously released because it had the pinhole problem). I guess I will trace the coolant water hoses from the reservoir and radiator and see where the problem is. Hopefully it's not the water pump or worse... valleypan.

Any suggestions, tips on what to look for beyond the obvious :-) Anyone know a good BMW indy mechanic in SF?