Aircon Leaking Water? Causes, Urgency & Repair Options

Why Your Aircon Is Leaking Water

Every aircon produces water as a normal part of its cooling process. When warm, humid air from your room passes over the cold evaporator coil, moisture condenses on the coil surface — just like water droplets forming on a cold glass. In Singapore’s tropical climate, with humidity often exceeding 80%, a single aircon unit can produce 1-2 litres of condensation per hour.

This water is designed to drip into a drainage pan beneath the evaporator coil, flow through a drain pipe (also called a drain hose), and exit the building at a designated discharge point. When any part of this drainage system fails, water has nowhere to go — and it leaks into your home.

Understanding the specific cause matters because the repair approach is different for each. Here are the most common causes, ranked by frequency.

Cause 1: Clogged Drain Pipe (Most Common)

The drain pipe carries condensation from the indoor unit to the discharge point. Over time, dust particles that pass through the air filter, algae that grows in the damp pipe, and sludge from the drainage pan accumulate inside the pipe. Eventually, the blockage restricts or completely stops water flow.

When the drain pipe is blocked, water backs up into the drainage pan. Once the pan overflows, water drips from the indoor unit — typically from the front panel, the bottom edge, or the louvres.

How we fix it: We disconnect the drain pipe and flush it with pressurised water or use a flexible cleaning tool to clear the blockage. For severe blockages with hardened algae or sludge, we may replace a section of the drain hose. After clearing, we pour water through the system to verify free flow.

Prevention: Regular aircon servicing every 3 months includes drain pipe flushing, which prevents blockages from building up.

Cause 2: Dirty or Damaged Drainage Pan

The drainage pan sits directly beneath the evaporator coil, catching all condensation before it enters the drain pipe. Over years of use, the pan can accumulate a layer of sludge and biofilm that clogs the drain outlet. In some cases, the pan itself cracks or warps due to age, temperature cycling, or poor material quality.

A cracked pan allows water to escape before it reaches the drain pipe. A sludge-clogged pan outlet causes the same overflow effect as a blocked drain pipe.

How we fix it: We remove the front panel and inspect the pan. If it is clogged, a thorough cleaning — or a chemical wash for heavy buildup — clears the issue. If the pan is cracked, we replace it with a compatible part. For some older models, we may need to order the replacement pan from the manufacturer, which takes 1-3 working days.

Cause 3: Insulation Damage on Copper Piping

Copper piping connects your indoor unit to the outdoor condenser. This piping carries extremely cold refrigerant and must be wrapped in foam insulation to prevent condensation from forming on the pipe surface.

When insulation deteriorates — due to age, sun exposure on external sections, or damage during servicing — the bare copper pipe is exposed to warm, humid room air. Condensation forms on the exposed surface and drips. This type of leak appears as water dripping from the wall, ceiling, or areas where piping runs, rather than directly from the indoor unit itself.

How we fix it: We identify the sections where insulation is damaged or missing and wrap them with new foam insulation tape. For piping that runs inside trunking, we open the trunking, re-insulate, and reseal.

Cause 4: Incorrect Drain Slope

The drain pipe must slope downward from the indoor unit to the discharge point. Even a slight upward section or a flat section creates a low point where water pools instead of flowing out. This is typically an installation problem — either the original installer did not route the pipe correctly, or the pipe has shifted over time.

How we fix it: We re-route the drain pipe with a consistent downward gradient. In some cases, a condensate pump may be needed if the discharge point is higher than the indoor unit (common in some condo installations where the drain exits through the ceiling void).

Cause 5: Low Refrigerant Causing Ice Buildup

When refrigerant gas is low, the evaporator coil temperature drops below freezing. Ice forms on the coil, and when the aircon cycles off or the ice becomes heavy enough, it melts rapidly. The sudden rush of water overwhelms the drainage system, causing overflow and leaking.

Signs: You may notice the aircon alternating between cold and warm air. Ice may be visible on the copper piping near the indoor unit. When the aircon is turned off, a large amount of water drips as the ice melts.

How we fix it: We address the underlying gas issue first. This typically involves leak detection, repair, and a gas top-up. Once refrigerant levels are correct, the ice problem stops, and drainage returns to normal.

Urgency Levels: When to Act

Not all water leaks are equally urgent. Here is how to assess yours:

High Urgency — Act Immediately

• Water dripping onto electrical outlets, power sockets, or light fixtures
• Water pooling on wooden flooring (causes permanent warping within hours)
• Water leaking near electrical appliances or wiring
• Continuous dripping that is getting worse

Turn off the aircon immediately and contact us for emergency service.

Moderate Urgency — Schedule Within 1-2 Days

• Slow drip from the indoor unit onto a hard floor (tile, vinyl)
• Water stains appearing on the wall or ceiling near the aircon
• Occasional dripping that stops when the aircon is turned off

Place a towel or bucket to catch drips and schedule a repair appointment.

Low Urgency — Address During Next Servicing

• Very occasional single drops after extended running
• Small moisture patch on the wall that dries quickly
• Water only appears during extremely humid weather

Mention this to your technician during your next regular service.

What Happens If You Ignore a Water Leak

Ignoring an aircon water leak leads to escalating damage:

Week 1-2: Water stains on walls and ceiling. Cosmetic damage only at this stage.

Month 1-2: Mould begins growing behind the wall or inside the ceiling cavity. Mould thrives in Singapore’s warm, humid conditions and spreads quickly once established.

Month 3+: Structural moisture damage. Paint peels, plaster softens, and wood components (door frames, skirting boards, parquet flooring) begin to warp. Mould colonies release spores that affect indoor air quality, particularly problematic for residents with asthma or allergies.

Worst case: Water reaches electrical wiring or components, creating a short circuit or fire risk. This is rare but represents the most serious consequence of a prolonged, ignored leak.

The cost of repairing property damage from an ignored water leak almost always exceeds the cost of fixing the aircon leak itself. Early action saves money.

Preventing Water Leaks

The best defence against water leaks is regular aircon servicing and preventive maintenance:

1. Service your aircon every 3 months. Each service includes drain pipe flushing, which is the single most effective way to prevent the most common type of leak.

2. Clean your air filter every 2-3 weeks. A clean filter means less dust reaching the drainage system, reducing sludge buildup in the pan and pipe.

3. Do not block the outdoor drain discharge point. Make sure the pipe exit is clear and not submerged in standing water. In HDB flats, check that the discharge tray on the aircon ledge is clean and draining properly.

4. Monitor for early signs. A slight musty smell, occasional single drops, or a humid feeling near the indoor unit can be early warning signs of a developing drainage issue.

Book Emergency Leak Repair

Billy Aircon treats every water leak call as a priority. Contact us for same-day service across Singapore. Our technicians arrive with the tools and parts needed for most common leak repairs — drain clearing equipment, replacement drainage pans, insulation materials, and condensate pumps. We diagnose the cause, fix it properly, and back the repair with a 90-day warranty.