AC Leaking Water?
Here's Why, by Unit Type

That points squarely at the condensate drain line. Central AC removes humidity from the air as it cools, and that water has to go somewhere — normally down a drain line to the outside. Algae and mold build up inside that line over time and eventually block it, so the water backs up and finds another way out, usually through the drain pan overflow. It only shows up when the system is running because that is the only time it is actually producing condensate.

In many systems, the furnace and the AC evaporator coil sit in the same air handler and share a single condensate drain line — the coil is often mounted directly above or beside the furnace. If that shared line clogs, the water has to come from somewhere, and it commonly shows up around the furnace even though the furnace itself is not the source. This is one of the most misdiagnosed HVAC leaks: people replace or service the furnace when the actual problem is the drain line the two systems share.

For a short time while you diagnose it, generally yes — a condensate leak is not usually a safety hazard the way a refrigerant or electrical problem would be. But keep water away from any electrical components, and don't let it run long enough to soak drywall, subfloor, or a ceiling below the unit. If the unit is in an attic, treat it as more urgent — attic leaks often go unnoticed until there is visible ceiling damage.

EPA guidance recommends drying wet materials within 24 to 48 hours specifically because mold can begin growing in that window on damp drywall, wood, or insulation. That is a planning benchmark, not an exact trigger — it depends on temperature and humidity — but it is the number worth planning around rather than waiting to see what happens.

Often, yes. The common DIY approach is to locate the drain line access point (usually a T-shaped fitting near the indoor unit) and clear it with a wet/dry vacuum from the outside termination point, or flush it with a cup of distilled vinegar to break down algae growth. If the clog keeps coming back, or you find standing water inside the unit itself, that points to something beyond a routine clean and is worth a technician visit.

The commonly cited range is a quarter to a half inch of drop toward the outside across the depth of the unit — enough for gravity to carry condensate out the rear drain holes, not so much that it stresses the mounting or unbalances the internal drain pan. But check your manual first: many newer window units, particularly inverter and U-shaped models, are designed with internal drainage that works with the unit level, and some manufacturers explicitly instruct not to tilt them. If your unit is one of those and it is leaking, tilting it is not the fix.

That depends on your lease and your local tenancy laws, so this is not legal advice — but practically, clearing a blocked drain line on a unit you control is usually reasonable tenant maintenance, while anything involving the building's central HVAC, a failed condensate pump, or resulting water damage is normally the landlord's. The useful move either way is to document it early: photos, the date you noticed it, and a written maintenance request rather than a verbal one.