2004 Ford Taurus sudden loss of MPG and water leaking from

24V DOHC
2004 Taurus SES 79,500 miles

I experienced a sudden loss of power and a decrease of 7 mpg and I noticed a leak from where the exhaust pipe meets up with the muffler, near the driver's side rear tire. The leak seems to just be water, doesn't have a fuel smell to it, but its a lot of water, enough that its changed the color the front part of the muffler to black, and when I drive slow (like pulling in the driveway after coming home from work) you can see the wet drops every 1-2 feet, then a small puddle under the front of the muffler.

i'm thinking the leak and the loss of power are related, but i'm not sure, what could be causing my problems? I was just about to change the spark plugs as I forgot to do that at 60,000 miles, but the only other maintenance items i've missed are flushing the brake fluid and radiator.