Window AC Unit Dripping Water Inside? Here's How to Fix It

Why Your AC Is Leaking (And Why It's Normal to Make Water)

First, a reassuring fact: your air conditioner is supposed to make water. It is literally pulling moisture out of the air. On a humid day, a window unit can produce one to two gallons of condensation. If your dehumidifier is also running but not lowering humidity, your home may have a more significant moisture issue worth investigating. That water is supposed to drip out the back of the unit, outside your home.

When water shows up inside instead -- dripping from the front of the unit, pooling on your windowsill, or running down the wall -- something is preventing proper drainage. The good news is that the most common causes are simple to fix yourself.

I have dealt with this in my own home more than once, usually on the hottest day of the year when I least want to be troubleshooting. So let me walk you through the fixes in order of likelihood.

The Most Common Causes

Improper tilt. Window AC units need to be tilted very slightly backward -- about half an inch lower in the back than the front. This lets gravity pull condensation toward the rear drain. If the unit is level or tilted forward, water pools at the front and drips inside.

Clogged drain hole. Every window unit has a small drain hole or channel at the bottom rear. Over time, dirt, algae, and debris block it. Water backs up and overflows into your room.

Dirty air filter. When the filter is clogged, airflow drops. The evaporator coil gets too cold and can ice up. When the ice melts, it overwhelms the drainage system and you get a puddle.

Damaged or missing drain pan. The pan that catches condensation underneath the coils can crack over time, especially in older units. Less common, but worth checking.

Very high humidity. On extremely humid days, even a perfectly working unit can produce more condensation than it can drain. This is usually temporary.

Step-by-Step Fix

Work through these in order. Most people find their answer in the first two steps.

Preventing Future Leaks

Once you have fixed the immediate problem, a few habits will keep it from coming back:

• Clean the filter every two weeks during summer. Set a reminder on your phone. A clean filter is the single most impactful maintenance step.
• Check the tilt at the start of each season. Units can shift over time, especially if the window gets opened and closed.
• Clear the drain hole once a month. A quick poke with a pipe cleaner takes five seconds.
• Run the unit on fan-only for 15 minutes before shutting it off for the season. This dries out the interior and reduces mold risk during storage.
• Keep the area around the unit clear. Curtains or furniture pressed against the front panel restricts airflow, which leads to icing and overflow.

When to Call a Professional

Most window AC leaks are genuinely easy to fix yourself. However, there are a few situations where you should call a technician or consider replacing the unit:

Refrigerant issues. If the coils ice up repeatedly even with a clean filter and good airflow, the unit may be low on refrigerant. This is not something you can fix yourself -- it requires a licensed HVAC technician. On older window units, the cost of a refrigerant recharge often exceeds the cost of a new unit.

Persistent mold inside the unit. If mold keeps returning inside the unit despite cleaning, the internal drainage system may be compromised. Some window units can be disassembled and deep cleaned, but many are not designed for easy internal access.

Physical damage. A badly rusted drain pan, a cracked housing, or a unit that has been dropped may have damage that is not worth repairing.

The unit is more than ten years old. Newer window AC units are significantly more energy-efficient. If an older unit is giving you trouble, replacing it often makes more financial sense than repairing it, especially when you factor in the electricity savings.

A Quick Note About Portable AC Units

If you have a portable (floor-standing) AC unit instead of a window unit, the same principles apply with one addition: most portable units have an internal reservoir that you need to empty manually when it fills up. If your portable unit stops running or starts leaking, check the reservoir first. Some models have a continuous drain option where you can attach a hose to route water to a floor drain. If your unit supports this and you are tired of emptying the tank, it is worth setting up.

Window AC leaks feel urgent -- nobody wants water dripping on their floor in the middle of summer. But in almost every case, the fix is straightforward. Start with the tilt, clear the drain, clean the filter, and you will likely be back to cool, dry air within the hour.

If your home has temperature inconsistencies too, check out why one room might always be colder than the rest.

Related: Dehumidifier Running But Humidity Not Dropping · One Room in House Always Colder · Thermostat Says One Temp But Feels Different