Why is my aircon leaking water? Common causes and fixes

Water dripping from your indoor air-conditioning unit is one of the most common aircon complaints in Singapore — and one of the most annoying, because it can stain walls, damage furniture and flooring, and in the worst cases reach a neighbour’s unit. The good news is that it’s almost always fixable without replacing the unit. This guide explains what causes an aircon to leak water, what you can safely check yourself, and when to call a technician.

How your aircon is supposed to handle water

It helps to understand what’s happening inside. As your air-conditioner cools the air, it condenses moisture out of it — that’s why the air feels dry. This condensation collects in a tray and drains away through a condensate pipe to the outside. When everything works, you never see a drop indoors. When water appears inside, it means that drainage system has been interrupted somewhere. Here are the usual culprits.

1. A blocked drainage pipe

This is by far the most common cause. Over time, dust, dirt and algae build up inside the condensate line, and eventually the water can’t flow away. It backs up into the tray and overflows into your room. Clearing and flushing the drainage line usually solves it completely — and it’s exactly the kind of build-up that regular servicing prevents.

2. Dirty coils and filters

When the filters and evaporator coil are clogged with dust, condensation forms unevenly and can drip off in the wrong places rather than running neatly into the tray. A general service or a chemical wash restores proper airflow and drainage, and often fixes a leak that seemed mysterious.

3. Low refrigerant (gas)

If the unit is low on gas, the coil can get too cold and freeze. When it later melts — for example when you switch the unit off — the sudden volume of water overwhelms the tray and drips out. Ice on the pipes or coil alongside a leak is a strong hint that gas is the issue, which needs a leak check and a top-up.

4. Installation or gradient problems

The indoor unit and the drainage pipe need to be installed at the correct angle so water flows away by gravity. If the unit isn’t level, or the pipe runs uphill or sags, water pools instead of draining. This is more common after a DIY installation or a relocation that wasn’t done carefully, and it needs correcting at the source.

5. A cracked or dislodged drainage tray

Less common, but a damaged or dislodged condensate tray can let water escape before it ever reaches the drain. This usually needs a technician to inspect and repair or replace the part.

What you can safely check yourself

Before calling anyone, you can safely do a few things: switch the unit off to stop the dripping and prevent damage; check and clean or rinse the filters, which is easy and sometimes enough; and look at where the drainage pipe exits outside to see whether water is actually coming out there (if not, the pipe is likely blocked). What you should not do is start dismantling the unit or poking objects into the drainage line — that risks damage and voids warranties.

Why you shouldn’t just keep wiping it up

A leak that keeps returning isn’t a cosmetic nuisance — the water can damage your wall, ceiling, flooring and any electronics below, encourage mould, and in an HDB or condo reach the unit downstairs. Because the cause is almost always a simple drainage or maintenance issue, it’s far cheaper to fix properly than to keep mopping and risk the damage spreading.

Frequently asked questions

Why does my aircon only leak sometimes? Intermittent leaks often point to a partial blockage or a freezing coil (low gas) that only overflows under certain conditions — still worth fixing before it worsens.

Can a leak fix itself? Sometimes a minor blockage clears temporarily, but the underlying build-up remains, so it usually returns. A proper clear-out is the lasting fix.

How do I stop it happening again? Regular servicing keeps the coils clean and the drainage clear, which prevents the most common cause. See how often to service your aircon.

Is a leaking aircon dangerous? The water itself is mainly a damage and mould risk, but water near electrical components is never ideal — switch the unit off and get it checked.

The bottom line

A leaking aircon is almost always a drainage or maintenance problem, not a reason to replace the unit. Switch it off, check the filters, and get the drainage cleared — and keep up regular servicing so it doesn’t recur.

Dealing with a dripping unit? See our aircon servicing and repair — we diagnose the cause, not just the symptom. Get a free quote today.

How regular servicing prevents leaks

Because the most common cause of a leaking aircon is a blocked drainage line or dirty coils, the single best prevention is regular servicing. A routine service clears the condensate line and cleans the coil before build-up gets bad enough to cause an overflow — which is why units on a maintenance schedule rarely leak. If yours has leaked once, it’s a good prompt to get onto a regular servicing cycle so it doesn’t happen again, especially before the hottest, heaviest-use months.

A few more questions

Can a leaking aircon damage my ceiling or a neighbour’s unit? Yes, if ignored — water can spread to walls, flooring and, in flats, downstairs. It’s worth fixing promptly.

Is it safe to keep using a leaking unit? Better to switch it off until it’s checked — water near electrical parts is best avoided.

Will a chemical wash stop the leaking? Often, if the cause is clogged coils or drainage; if it’s low gas or an install issue, that’s a separate fix.

What the leak can damage if ignored

It’s tempting to treat a small drip as a minor annoyance, but the knock-on costs add up quickly. Water running down a wall can blister paint, swell skirting and damage nearby carpentry; dripping onto flooring can warp laminate or lift vinyl; and moisture around the unit encourages mould that affects both the appliance and your indoor air. In an HDB flat or condo, a persistent leak can even reach the unit below and become an inter-floor issue. Because the underlying cause is almost always a cheap, simple fix — a cleared drainage line or a coil clean — it makes no sense to keep mopping up and risk far costlier damage to your home.