When your air conditioner is running, the last thing you expect is to find water pooling on your floor or dripping from the indoor unit. Unfortunately, an AC leaking water inside the house is a very common issue for homeowners, especially during the peak of summer.

While it might seem minor at first, this problem should never be ignored. Excess water can damage your walls, ceilings, flooring, and furniture. Worse, it creates the perfect environment for mold growth and poor indoor air quality.

In this guide, we’ll explain:

• How your AC normally handles moisture
• The top reasons why your AC leaks water indoors
• What you can do to fix it yourself
• When it’s time to call an HVAC professional
• Preventive steps to stop leaks before they happen

By the end, you’ll understand the problem, know what’s safe to try on your own, and how to avoid future issues.

How Air Conditioners Normally Handle Water

Your AC doesn’t just cool the air, it also reduces humidity from it. Here’s how the process works:

1. Warm indoor air passes over the evaporator coil: The coil is cold, so moisture in the air condenses into water droplets.
2. The condensation drips into the drain pan: The pan sits beneath the coil and catches the water.
3. The water flows through the condensate drain line: The line directs the water safely outside your home.

When this system works properly, you’ll never notice the water. But if any part of this process fails, water can back up and leak into your house.

7 Common Causes of an AC Leaking Water Inside

1. Clogged Drain Line

This is one of the most common reasons for an AC to leak water. The moisture collected by your unit during the dehumidification process contains dirt and debris. Over time, if the condensate drain line is not cleaned, this buildup can cause a blockage. When the line is blocked, water can’t escape and instead overflows inside your home.

Signs of a Clogged Drain Line:

• Water pooling around the indoor AC unit
• Gurgling or bubbling noises near the drain line
• Musty odors from mold inside the line

How to Fix:

• Turn off and unplug the AC for safety.
• Locate the drain line (position depends on your AC model).
• For mild clogs, scrub with a long wire brush or flush with vinegar.
• For stubborn clogs, use a wet/dry vacuum to suck out debris.

Preventive Tip: Pour a cup of vinegar or diluted bleach into the line every 6 months to keep it clear. Do not overdo this, as excessive bleach may cause corrosion.

2. Dirty or Frozen Evaporator Coils

When airflow is restricted or the coils get dirty, they can freeze. Once the ice melts, it produces more water than the system can handle, leading to leaks.

Signs of Frozen or Dirty Coils:

• Weak airflow or warm air from vents
• Visible frost or ice on the indoor unit
• Higher energy bills without better cooling

How to Fix:

• Switch off the AC and let the ice melt completely.
• Replace the air filter to restore airflow.
• Clean coils carefully with a soft brush or coil cleaner (for light dirt).
• If coils continue to freeze, call an HVAC technician, it could be a refrigerant or airflow issue.

Preventive Tip: Replace your air filter every 30–90 days and schedule annual coil cleaning.

3. Cracked or Rusted Drain Pan

The drain pan collects condensation from the evaporator coil. Over time, it can crack or corrode, especially in older systems, letting water escape instead of draining properly.

Signs of a Damaged Drain Pan:

• Water leaks even when the drain line is clear
• Rust spots or visible cracks in the pan
• Puddles of water forming directly under the unit

How to Fix:

• Inspect the pan for cracks or rust.
• Small cracks can sometimes be sealed with epoxy, but this is temporary.
• For lasting results, have a technician replace the drain pan.

Preventive Tip: During annual maintenance, ask your HVAC technician to inspect the drain pan and replace it before it becomes a problem.

4. Low Refrigerant Levels

When refrigerant is low, it lowers the pressure inside your AC, which can cause coils to freeze. As the ice melts, excess water spills inside your home.

Signs of Low Refrigerant:

• Hissing or bubbling sounds from the system
• Weak cooling or warm air from vents
• Ice buildup on refrigerant lines or coils

How to Fix:

• Only licensed HVAC professionals can recharge refrigerants and fix leaks safely.
• Continuing to run the system with low refrigerant may damage the compressor.

Preventive Tip: Schedule regular inspections to detect refrigerant leaks early, this avoids expensive compressor damage.

5. Improper AC Installation

If your AC wasn’t installed correctly, problems like an uneven unit or poorly connected drain lines can prevent water from draining properly.

Signs of Poor Installation:

• Water leaks soon after a new AC installation
• Persistent leaking even after cleaning the drain line
• Loud or unusual noises during operation

How to Fix:

• A technician needs to re-level the unit or reinstall the drain line.
• In severe cases, the system may need partial reinstallation.

Preventive Tip: Always hire licensed and experienced HVAC installers. Poor installation is one of the top causes of ongoing AC problems.

6. High Indoor Humidity

In humid climates, the AC must work extra hard to remove moisture from the air. If condensation builds up faster than the system can drain it away, leaks can occur.

Signs of Excess Humidity:

• Your home feels damp or sticky even with AC on
• Water dripping near vents or ductwork
• Frequent water accumulation around the air handler

How to Fix:

• Install a whole-home dehumidifier to reduce excess humidity.
• In some cases, upgrading to a newer AC system with better moisture control is needed.

Preventive Tip: Use exhaust fans in kitchens and bathrooms, and seal air leaks around windows and doors to keep humidity in check.

7. Clogged Air Filter

A dirty air filter blocks airflow, causing coils to get too cold and freeze. When the ice melts, it produces excess water that can overflow.

Signs of a Clogged Air Filter:

• Weak or no airflow from vents
• Coils freezing frequently
• Higher energy bills and poor cooling efficiency

How to Fix:

• Replace air filters every 1–3 months, depending on usage and indoor air quality.
• For homes with pets or allergies, monthly replacement is recommended.

Preventive Tip: Set a reminder on your phone or calendar to check filters monthly, it’s the simplest way to prevent leaks and keep your AC efficient.

The Risks of Ignoring a Leaking AC

It may be tempting to place a towel under the leak and ignore it, but this can lead to serious problems:

• Mold and mildew growth → leading to poor indoor air quality and health issues.
• Water damage → ruining drywall, ceilings, and flooring.
• Structural damage → long-term leaks can weaken wood framing.
• Electrical hazards → water near your AC’s electrical components is dangerous.
• Complete system breakdown → if the cause is refrigerant-related, your AC could stop working altogether.

How Much Does It Cost to Fix a Leaking AC?

Fixing a leaking AC can cost anywhere from $100 to $1,200, depending on the cause and severity of the problem.

Cost table for AC fixes

Routine maintenance ($100–$200 annually) is much cheaper than major repairs.

Preventing Future AC Leaks

The best way to avoid AC water leaks is with regular maintenance. Here are some prevention tips:

• Change your air filters every 30–90 days.
• Schedule professional HVAC tune-ups once a year.
• Ask about installing a float switch, it shuts off your AC if water backs up.
• Keep your condensate line clear with vinegar flushes.
• Use a dehumidifier if you live in a humid region.

Prevention not only saves you from costly repairs but also keeps your home safe from water damage.

What to Remember:

An AC leaking water inside the house is usually a sign that something in your system isn’t working as it should. Whether it’s a clogged drain line, frozen coils, or a refrigerant issue, the key is to act quickly before it causes damage to your home.

Small maintenance tasks like changing air filters and cleaning the drain line can often fix minor problems. But for more serious issues, like refrigerant leaks or installation errors, it’s best to call a licensed HVAC technician.

Remember, what starts as a few drops of water today can turn into expensive damage tomorrow. Stay proactive with maintenance, and your AC will keep your home cool, dry, and comfortable all summer long.