A little water is normal especially in colder weather. It is not likely that it is coolant coming out of the exhust, if it was you'd have a lot of other symptoms.
If you vehicle is leaving a noticeable black dusty or dark damp patch behind then this may indicate an issue. Along with that if your mileage has taken a slight dip as well as your vehicles power is a definite sign of a problem.
This can happen when your engine is running too rich. Most likely causes for this either relate to ignition system issues, like one cylinder not firing correctly, or O2 sensors. If your O2 sensors are providing incorrect information to the ECM your engine will run to rich. This should problem should not go long unchecked as it will cause your catalytic converter, muffler, and other exhaust components to become caked with soot. Also, your O2 sensors will become coated with soot and give off even worse readings further aggravating the issue.
See this link for troubleshooting 02 sensors. This link is good too.
Most of the time you can verify this with a code-reader. Most of time this will not throw up a engine light, but the ECM will notice inconstant readings. See diagram below.
Before you have it serviced or replace parts check the codes for any indications of it running too rich. If you have the other symptoms and are getting error codes, I would suggest inspect/replace your spark plugs and, depending on the mileage on them, then your O2 sensors. If you are a DIY-er then you may need a special socket to remove the sensor. This is what my socket looks like:
They can be a real pain to remove. You may have to heat it with a torch and use a breaker bar in conjunction with a cheater pipe.
Most likely it is not more serious than that but sometimes if your exhaust manifold has a hole or crack in it or you have a hole in your exhaust pipe upstream from the O2 sensor then this can also cause it to run too rich as the sensors report too much air and not enough fuel in the exhaust. You should be able to hear this as well as see the breach. Inspect your pipe.