The water that drains from a central air conditioning unit is condensate that has accumulated on the cooling coils within the unit. Air conditioners pull humidity out of the air and funnel the resulting water, or condensate, into a drain. the amount of condensate the unit produces varies, increasing as the outdoor humidity level rises. Most modern air conditioners will produce between 5 and 20 gallons of water per day. Increasing water drainage from your air conditioning unit is not something to worry about unless you notice a dramatic increase or decrease without a corresponding change in humidity. If that happens, it's time to call the repairman.
Condensation accumulates in your air conditioner as the unit cools the air. Indoor air is circulated across coils filled with cold refrigerant. These coils accumulate condensation just as a bottle of cold water does in a hot room. The water then drips down into a pan and drains outside the home. This is a byproduct of the cooling process and is not cause for concern.
Humidity measures the amount of water vapor present in the air. On days where the humidity is higher, you may notice an increase in the amount of water your air conditioner is draining. This is completely normal and is an artifact of the air conditioning removing more water from the air. There is no other water in the air conditioning system that can be leaking, so any water emanating from your central air conditioning unit is harmless condensate.
Overflowing Drain Pan
You will want to keep an eye on your air conditioner's drain to ensure that water is continuing to flow freely. The pan within the unit that gathers the dripping condensate can clog. Small amounts of debris or hair will clog the drain, as can algae growth. If the drain clogs, water will back up and leak. In most modern units this flips a switch, turning the unit off. In older installations, however, this feature may be absent. To avoid a clogged drain, inspect your unit's drain pan and line at the start of the cooling season and clean them if necessary. If you don't feel comfortable doing the job yourself, contact a local HVAC company to do it for you.