Did you know that it's possible to have a leaky furnace? 'Tis true.  Up until recently I thought leak = trouble with my water tank.  Apparently this is not always the case, as I discovered in my basement.  It wasn't a lot of water, just a little bit, but as my hot water tank and furnace are side by side, I just automatically assumed the water heater to be the culprit.  My hot water tank is a rental, so I jumped on the phone demanding that they send someone out to fix this problem.  They had me check this hose, this spout, this connection...no leakage from any of those.  I said the water was coming from under the tank, they said, "Ma'am, it is not possible for your hot water tank to leak from the base - is your furnace standing right next to it? You might have to call an HVAC service person."  Ack!  Of course, immediately I saw dollar signs and imagined my pocket book becoming significantly lighter in a short period of time.  I knew nothing about furnace repair and assumed I was looking at a monstrous bill to fix mine...or worse, that they would tell me it was time for a replacement.

Before losing my cool, and money that I would rather not part with, I decided to do some research into the possible reasons for a leaky furnace. 

1) Check your air filter.  Apparently, if your air filter is dirty and you have your A/C pumped through your unit it can cause your condensate pump to freeze.  What does this mean? No condensation being pumped out of the unit and just leaking straight out of the bottom.  Change your air filter; recommended frequency is every 3 months.

2) If you think step 1 is the culprit, after you've changed your dirty air filter (insert sheepish look here) turn off your A/C to let the pump thaw and it should start working again.

3) If the pump is toast and just not working anymore, supposedly it is something relatively simple and inexpensive to replace.  I, with no knowledge of furnaces, would call an HVAC company at this juncture to replace it for me.

4) There should be a drainage hose running from the outside of the furnace to a drainage hole in the floor, check to make sure the hose is clear of debris or algae, and that it is connected properly.

If you follow all these steps and still the leaking persists, it is time to call an HVAC technician.  However, you can do so with the knowledge that you did take every step possible before giving in...

As for me? It turned out that my hose had somehow become disconnected from where is was supposed to be, so obviously not doing its job properly.  The errant piece has now been reconnected and it seems like problem solved. 

Good luck!