An air conditioner leaking water inside an apartment is a problem made more urgent by the fact that you may not own the apartment, you may not own the AC, and the water may leak into the apartment below yours before you even notice it. Apartment AC leaks fall into three categories depending on the type of equipment: a window unit you bought and installed yourself, a through-wall unit that belongs to the building, or a portable unit on casters. The causes for each are similar to a central AC leak, a clogged drain path, a dirty filter causing coil freeze, or the unit not being level, but the fixes are different because you may not have access to the outdoor portion of the system, you may need permission to do repairs, and the person responsible for the repair may be the landlord, not you.
The first decision is whether this is your problem to fix or the landlord’s. If the AC is a window unit or a portable unit that you own, it is your problem. If the AC is a through-wall unit or a central system that came with the apartment, it is almost certainly the landlord’s problem. Read your lease. Most leases make the landlord responsible for maintaining appliances and systems that were provided with the apartment. A window unit you purchased is your property and your responsibility. Before you do anything that involves opening the unit or modifying the building, such as drilling new mounting holes or running a drain line through the wall, get permission from the landlord in writing. A well-intentioned repair that damages the building can cost you your security deposit.
EPA WaterSense advises that detecting and fixing leaks quickly prevents damage to your home and wasted water. In an apartment, a leaking AC can damage not only your unit but the units below. Report the leak to your landlord immediately if it is their equipment. If it is yours, fix it before it becomes a larger problem.
Window AC Leaking Water Inside
A window air conditioner is designed to drain condensation out the back of the unit, which hangs outside the window. The unit must be installed with a slight tilt toward the outside, typically a quarter to half an inch, so that water flows to the back of the drain pan and out the rear drain holes. If the unit is level or tilted toward the inside, water pools in the front of the pan and leaks into the room. The tilt is the most common cause of a window AC leaking indoors.
Check the tilt with a level placed on top of the unit. The unit should slope toward the outside. If it does not, adjust the mounting. Window ACs are supported by the window sill on the bottom and the window sash on the top, with side brackets that attach to the window frame. Adding shims under the front edge of the unit, thin pieces of wood or plastic, tilts the unit outward. The shims must be secured so they do not work loose from vibration. Most window AC mounting kits include a bracket that sets the correct tilt automatically when installed correctly. If your unit was installed without the bracket, or if the bracket has slipped, reinstalling it correctly may solve the leak.
The rear drain holes can become clogged with dirt, leaves, or insect nests. The water has nowhere to go and overflows into the room. Check the drain holes on the bottom rear of the unit. Clean them with a wire or a small screwdriver. Some window ACs have a drain plug that can be removed for drainage. If the plug is in place, remove it during the cooling season and replace it only when storing the unit for the winter.
Through-Wall AC Leaking
A through-wall air conditioner is a permanent unit installed in a sleeve that passes through the exterior wall. The unit is typically owned by the building and is the landlord’s responsibility to maintain. The causes of a through-wall AC leaking indoors are the same as a window unit: the unit is not level, the drain holes are clogged, or the drain pan inside the unit is cracked or rusted through.
Check the tilt. A through-wall unit should be level or tilted slightly toward the outside. If the unit has shifted, the sleeve may need to be adjusted. The sleeve is mounted to the wall framing and may require a contractor to reposition. This is not a tenant repair. Report it to the landlord.
Check the filter. Through-wall units have a washable filter behind the front grille. If the filter is clogged, airflow is restricted, the coil freezes, and the meltwater overwhelms the drain pan. Clean the filter. This is a tenant task. Clean it monthly during the cooling season. A clogged filter is the most common cause of a through-wall AC leak that a tenant can fix without involving the landlord.
Portable AC Leaking
A portable air conditioner collects condensation in an internal reservoir. Most portable units are designed to evaporate the condensate back into the exhaust air, eliminating the need for a drain. In humid conditions, the unit produces more condensate than it can evaporate. The reservoir fills. The unit may shut off automatically, display an error code, or leak water onto the floor.
Empty the reservoir. Locate the drain plug, typically on the bottom or the back of the unit. Place a shallow pan under the plug and remove it. The water will drain out. Replace the plug. Some portable ACs have a continuous drain option. A garden hose or a vinyl tube connects to the drain port and runs to a floor drain or a large container. If you are using the unit in a consistently humid environment, set up the continuous drain.
Portable ACs also have washable filters. Clean them every two weeks during heavy use. A dirty filter reduces airflow, causes the coil to run colder, produces more condensation, and fills the reservoir faster. The filter is behind the front grille and lifts out without tools.
Central AC in an Apartment Building
If your apartment has central air conditioning, the indoor unit, the air handler or the fan coil, is likely in a closet, a ceiling, or a mechanical room. The outdoor unit is on the roof or in a mechanical yard that you do not have access to. If the indoor unit is leaking water, the cause is almost always a clogged condensate drain line. The fix requires accessing the drain line, which may be inside the unit behind an access panel. This is a landlord repair. Report the leak. Turn the AC off to stop the water production while you wait for maintenance to arrive. Place a bucket or towels under the leak to protect the floor.
If the apartment has a heat pump or a fan coil that serves only your unit, you may have access to the filter. Change it if you can access it. A dirty filter can cause the coil to freeze and leak, the same as any AC. If the filter is in a ceiling return grille, it is a tenant task. If it is inside the equipment cabinet, it may require a maintenance request. Know where your filter is and whether you are allowed to change it.
Frequently Asked Questions
Should I call the landlord or fix the AC leak myself?
If the AC is a window unit or portable unit that you own, the repair is your responsibility. If the AC came with the apartment, a through-wall, central, or mini split system, the repair is the landlord’s responsibility. Report the leak immediately. Water damage to the apartment below yours is a liability issue. Document the leak with photographs and a written report to the landlord. If the landlord does not respond promptly, follow up. A paper trail protects you if the leak causes damage that the landlord later tries to attribute to your negligence.
What if the AC is leaking into the apartment below mine?
Turn the AC off immediately. Report the leak to the landlord. The water is traveling through the wall or the floor and causing damage that you cannot see. The landlord needs to address both the AC repair and any water damage to the building structure. Your renters insurance may cover damage to your personal property from an AC leak. It will not cover damage to the building, which is the landlord’s insurance. Report the leak before it becomes a claim.
My window unit can’t tilt outward because the window is configured oddly. What can I do?
Install a condensate drain kit. Some window ACs have an optional drain fitting that screws into a threaded hole in the bottom of the drain pan. A vinyl tube attaches to the fitting and runs to a floor drain, a bucket, or out the window below the unit. The drain kit eliminates the need for the tilt by providing a direct path for the water. If your unit does not have a threaded drain port, you can drill a small hole in the lowest point of the drain pan from the inside of the unit. This is a permanent modification. Do it only if you own the unit and are comfortable with disassembling it.
The Bottom Line
An AC leaking water in an apartment is either your problem or the landlord’s problem, depending on who owns the equipment. Check the tilt of a window unit. Clean the filter of any unit. Clear the drain holes on a window or through-wall unit. Empty the reservoir on a portable unit. Report a leaking central or through-wall unit to the landlord immediately. The water from a leaking AC can damage the apartment below, and the liability for that damage depends on who was responsible for the repair. Fix what is yours to fix. Report what is the landlord’s to report. Do not modify the building without written permission. The fastest fix for a leaking AC is usually the simplest: check the tilt, clean the filter, clear the drain.
Last modified: July 7, 2026
