Is AC Water Harmful? Why Air Conditioners Drip

If you’ve seen water dripping from a window unit or a pipe running from your central AC, you might wonder whether your air conditioner uses water. It doesn’t. It makes water.

Where AC water comes from

An air conditioner cools air by blowing it across a very cold coil (the evaporator). Warm, humid air hitting the cold coil drops its moisture as condensation, the same way a cold glass “sweats” on a summer day. The water drips into a pan and drains away:

• Window units drain out of the back of the unit, outside.
• Central air drains through a pipe (the condensate line) to a floor drain, outside, or into a small pump.
• Portable ACs either evaporate the water into the exhaust hose, collect it in a tank you empty, or drain through a hose.

This is why air conditioners also make a room feel less muggy: removing moisture is part of how they work.

How much water does an AC produce?

It varies a lot with humidity, the size of the unit and how long it runs. On a hot, humid day a home system running for hours can produce several gallons; in a dry climate, very little.

Is AC water safe to drink?

No. Condensate starts out close to distilled water, but it runs over coils, pans and drain lines that can harbour bacteria and mould, and it can pick up traces of metal from the coil. It isn’t treated or tested like drinking water. Don’t drink it or give it to pets.

Can you use AC water on plants?

Generally yes, for ornamental plants, lawns and flower beds, with a few precautions:

• Don’t use it after the coil has been chemically cleaned or treated with algaecide tablets, since residues end up in the water.
• Skip edible plants if you are unsure about the unit’s condition.
• Mix it with tap water or rainwater now and then. Condensate has almost no minerals, so plants watered only with it may need regular feeding.

Why is my air conditioner leaking water inside?

Some dripping outside is normal. Water inside is not. The usual causes:

1. A window unit isn’t tilted correctly. Most window units need to slope slightly down toward the outside so water runs to the back. LG recommends a tilt of about 1/4 to 1/2 inch from front to back. Some newer units have a sloped pan and should be installed level, so check the manual.
2. A blocked drain hole or drain line. Dirt, dust and algae can clog the drain so water backs up and overflows the pan. On central AC, a clogged condensate line can overflow into the house or trip a safety switch that shuts the system off.
3. A dirty air filter. Poor airflow can let the coil freeze. When the ice melts, there’s more water than the pan can handle.
4. A cracked or rusted drain pan, which usually needs a part replaced.
5. A failed condensate pump on systems that pump water away.

How to clear a clogged AC drain

• Window unit: Unplug it. Clean the filter, then clear the drain hole or channels at the back with a pipe cleaner or soft wire. Some units have a drain plug to remove.
• Central AC: Turn the system off at the thermostat. Find the condensate line where it exits the house or at the air handler. A wet/dry vacuum on the outside end often pulls out the blockage. Some lines have an access cap where you can flush them with water.

If the line keeps clogging, the pan is damaged, or water is near electrics, call an HVAC technician. Clearing a drain line is usually one of the cheaper service calls, but prices vary by area, so ask for a quote first.

Do any air conditioners actually use water?

Yes, but not usually in homes. Large commercial buildings often use water-cooled systems with cooling towers, and evaporative (“swamp”) coolers, which are not true air conditioners, cool air by evaporating water and work best in dry climates. A standard window, portable, mini-split or central air conditioner doesn’t need a water supply.