Why an air conditioner makes water
Cooling air removes moisture, and that moisture collects on the evaporator coil and drips into a pan. A drain line carries it outside or to a drain. When the line clogs with algae or sludge, the pan overflows and water goes where you do not want it, usually into a ceiling, a closet or onto the floor.
The water is clean enough to be mistaken for a supply leak. The difference is that condensate only appears while the system runs, and it often follows a pattern: a hot afternoon, the system runs for hours, and the stain grows.
Tell the source apart
| Clue | Condensate drain | Plumbing supply or drain leak |
|---|---|---|
| When water appears | Only while the AC runs | At any time, even with the AC off |
| Water meter with everything off | Does not move | Moves if a supply line leaks |
| Location | Under or near the air handler or its drain line | Near fixtures, walls or the slab |
| Water temperature | Cool | Cool or warm, depending on the line |
The meter test is the key. Turn off every tap and appliance, then watch the meter. If it does not move and water still shows up only when the AC runs, you probably have a condensate problem. If the meter moves, call us, because that is a true plumbing leak. Our leak detection page explains the tools we use.
What to check yourself
Turn the system off
Switch the thermostat to off to stop making water.
Check the pan
Look for standing water in the drain pan under the air handler.
Look at the drain outlet
Find where the condensate line ends, often near the foundation or a drain, and see if it is dripping.
Clear a simple clog
A wet-dry vacuum on the outlet end may pull out a plug. Do not force a stuck line.
Do not pour bleach or harsh chemicals through a line that connects to a plumbing drain without checking what it ties into. The wrong chemical can damage metal parts or fixtures.
When it is a plumbing leak after all
Water near a water heater
Attic and closet water heaters can leak into the same area as an air handler. See water heater repair.
Stain that grows with no AC use
A supply line or fixture leak above the ceiling.
Damp wall near a bathroom
Shower or tub leaks can look like AC drips.
Warm wet spot on a slab
A hot water line leak. See slab leak repair.
What a plumber can and cannot do
A plumber can find out whether the water is a supply, drain or fixture leak and fix it. We can also clear a condensate line that ties into a plumbing drain. We do not repair the air conditioner itself, so if the coil or pan is damaged, an HVAC technician is the right call.
We will tell you honestly which trade you need. Calling the wrong one costs time while the stain spreads.
Protecting your ceiling and your insurance claim
- Photograph the stain, the pan and the water source.
- Place a bucket or towels to stop the spread.
- Leave wet drywall open if you can so it dries, and call a restoration company if it sags.
- Tell your insurer promptly, and keep any damaged items until they are documented.
Preventing condensate trouble next summer
- Change the air filter on the schedule the system maker gives, since a dirty filter freezes the coil and then floods the pan when it thaws.
- Have the condensate line flushed once a year before the heavy cooling months.
- Check that the drain pan has a float switch or a secondary pan in attics.
- Keep the outlet end of the drain line clear of dirt and plants.
A float switch shuts the system off when the pan fills, which turns a ceiling stain into an inconvenience. If your attic unit has none, ask your HVAC technician about adding one. It is a small part with a large payoff.
Guidelines that apply
Condensate drains must terminate in an approved location under the California Plumbing Code, which is based on the Uniform Plumbing Code (UPC), and your air conditioner maker publishes guidelines for drain pan and float switch installation. Follow those before improvising a fix.
Pleasant Hill: reading your water use
Your water provider's meter is your best diagnostic tool. Contra Costa Water District serves parts of Pleasant Hill, and your bill names the provider that serves your address. A meter that does not move with everything off points away from a supply leak.
Homes in the area range from postwar tract houses near Contra Costa Boulevard to later subdivisions, and attic air handlers are common in many of them. Ask your water utility for its water quality report if you suspect mineral buildup is clogging lines.
If you are closer to Walnut Creek or Clayton, see the Walnut Creek page or the Clayton page.
Local questions
Most often the condensate drain is clogged with algae or sludge, so the pan overflows while the system runs.
Check the water meter with everything off. If it does not move and the water only appears while the AC runs, it is probably condensate.
Yes, when it ties into a plumbing drain. Repairs to the air conditioner itself belong to an HVAC technician.
It can grow algae and damage drywall. Dry the area promptly.
Yes, until the source is found, to stop making water.
Still have a question about your situation? Call (855) 575-2890 any hour and describe what you are seeing.