Many homeowners give little thought to water when it comes to their air conditioner. Since your AC is not connected to your plumbing or require water flow to operate you may not make a connection. Yet, water is a part of how air conditioners carry out the process of heat exchange. When the indoor evaporator coil absorbs the heat from inside your home, it creates water vapor that condenses across the coil. If you listen carefully, you may even hear a dripping sound as moisture drips down into a collection pan and is safely drained away. When your air conditioner is operating normally, you don’t need to give much consideration to water moisture. Unfortunately, if a something happens you may start to see puddles under your air conditioner that can indicate a problem has developed. 
Clogged Drain Lines:
In many cases, a puddle under your air conditioner unit is a simple matter of a drain line becoming clogged. Just like the drain connected to your bathtub or kitchen sink, the drain in the condensate pan may develop a clog that can slow down or stop water from being safely carried away. Since the condensate pan is so shallow, a blockage can cause an overflow in the pan very quickly, which will allow water to enter your home and create a puddle. In some air conditioner models, water overflow will trigger a sensor switch to shut off the system to prevent greater overflow. This problem usually has a quick fix of checking the pan and drain line and removing any obstruction.
Detached Pan or Drain:
If the pan or drain has become disconnected, a similar problem can develop. Since the water cannot properly drain away, it overflows and puddles under the unit. This is a less common problem. It usually occurs if the pan has been dislodged due to an amateur tampering inside the cabinet. In some cases, the drain can become corroded and break off. This is a more serious issue as water will begin to spill out directly. This is very problematic particularly if you have electrical items located underneath. It can also cause damage to flooring or even contribute to mold and mildew.
Faulty Condensate Pump:
The pump in your condenser is electrically powered and is located where the drain line collects condensate. When the water collection reaches a specific level, the pump is triggered to push the water out of the system. Like any pump, the condensate pump will not last forever, and if it burns out, it will need to be replaced. If the pump has begun to fail, you may notice strange straining noises or a burning smell coming from the air conditioner unit. Once the pump has failed, the system will not operate, so you will not be able to turn your air conditioner on.
Water puddling should not be ignored. Although it is easy to wipe up a small amount of water and forget about it, it is a symptom that something is wrong with your air conditioner. Condensate problems can not only threaten to prevent your air conditioning from working, but it can lower your air quality and cause damage to your home.