An air conditioner leaking water from the indoor unit usually means the condensation it collects can’t drain away. The common causes are a blocked drain line, a dirty filter that lets the coil freeze and then thaw, a unit that isn’t level, or a cracked drain tray. Switch the unit off if water is running near a power point, and put a towel under it while you check.
Water from the outdoor unit is normal. In cooling mode the drain hose outside should drip steadily on a humid day, and in heating mode the outdoor unit sheds water when it defrosts.
Is it safe to keep running?
A few drips onto a towel are not dangerous, but the water will keep coming while the unit cools. Stop using it if water is near electrical outlets, is running down the wall inside the plaster, or is dripping onto flooring that can swell. Switching to fan mode for an hour will thaw any ice without making more water.
Causes and what each one needs
| Cause | What you’ll see | DIY or technician |
|---|---|---|
| Blocked drain line (dust, slime, insects) | Drips from the bottom edge of the indoor unit; no water at the outside drain | Technician to clear and flush; DIY only if the outside end is simply blocked by dirt |
| Dirty filter causing a frozen coil | Ice on the coil or pipes, then a rush of water when it melts | DIY: clean filters, thaw in fan mode |
| Unit not level after installation or wall movement | Water runs out one side of the unit | Technician |
| Cracked or dislodged drain tray | Steady drip even with a clear drain | Technician |
| Drain hose kinked, crushed or running uphill | Leaks start after garden or building work | DIY check outside; technician to re-run |
| Low refrigerant | Coil keeps icing even with clean filters | Technician (ARCtick-licensed) |
| Condensate pump failure (some units) | Unit stops or leaks where water is pumped up and away | Technician |
How to check the drain line
- Find where the drain hose ends outside. It is usually a thin hose near the outdoor unit or running into a garden bed or gutter.
- With the unit in cool mode on a warm day, look for a steady drip from the end. No water while the indoor unit leaks means the line is blocked or kinked.
- Check the end isn’t buried in soil or mulch, crushed, or pushed up into a loop.
- Leave clearing inside the unit to a technician. Pushing wire into the drain can crack the tray.
Why leaks start after a service or in humid weather
A service loosens dirt and slime from the coil, and that can settle in a partly blocked drain line. Humid days also make far more condensation, so a drain that coped all year can overflow in one muggy week. Both point to the drain rather than a new fault.
Brand guides
When to call a technician
Book a technician if the leak continues after the filters are clean, if there’s no water from the outside drain, or if ice keeps forming. A drain clear and flush is part of every air conditioner service. You can book online, or see our troubleshooting hub for other faults.
In Australia, refrigerant work must be done by a technician who holds an ARC licence. You can read more about licensing on the ARCtick website.
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Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles