Home › Commercial Refrigeration Guide › Walk-In Cooler & Freezer Guide › Water on the Walk-In Floor or a Frozen Drain Line
Updated October 14, 2026
Quick answer
Water on a walk-in floor usually comes from the evaporator drain: a clogged or frozen drain line, a cracked or tilted drain pan, or a failed drain-line heater on a freezer. Condensation from door leaks and melting product ice are the other common sources. A frozen drain on a freezer will not clear on its own.
What you are seeing
In a cooler, you may see a puddle under the evaporator, water running down the wall, or drips during and after defrost. In a freezer, the same problem shows up as ice under the evaporator, a pan full of ice, and eventually ice growing up into the coil.
Puddles near the door, rather than under the evaporator, usually mean condensation from a door leak or melting frost off product.
Likely causes
| Cause | How to tell | Who fixes it |
|---|---|---|
| Clogged drain line (slime, debris) | Pan full of water; slow drip from the drain outlet | Technician; staff can keep the outlet clear |
| Frozen drain line (freezer) | Pan full of ice; ice in the line | Technician; drain heater usually failed |
| Drain line heater failed | Drain freezes repeatedly | Technician |
| Cracked or loose drain pan | Water drips from pan edges or seams | Technician |
| Evaporator not level | Water runs to one end and overflows | Technician |
| No trap or poor slope on the drain line | Gurgling; water backs up; warm air pulled into the box | Technician |
| Door leak condensation | Water near the door, frost on the frame | Technician; see door pages |
Safe checks you can do
- Look at the drain pan under the evaporator (with a flashlight; no need to open anything).
- Find where the drain line exits the box and check its outlet is not blocked or submerged.
- Note whether the water appears only after defrost.
- Mop the floor and put up a wet-floor sign; walk-ins are a common slip hazard.
- Do not pour hot water into a freezer drain pan; it can refreeze further down the line.
What the technician will do
- Clear and flush the drain line and clean slime from the pan.
- Test and replace the drain-line heater; on freezers, check it runs along the full length of line inside the box.
- Level the evaporator and repair or replace the drain pan.
- Correct the drain slope and add a trap outside the box where needed.
- Treat the pan with approved pan tablets if slime keeps returning.
Cooler vs freezer
Coolers drain by gravity and need only a clear line and pan. Slime is the main enemy.
Freezers need a heater along the drain line inside the box and often a heater in the drain pan, because meltwater refreezes within minutes. A freezer drain problem nearly always involves a heater fault.
How to prevent it
- Have the drain pan and line cleaned at each service visit.
- Keep the drain outlet clear of mop buckets, boxes and debris.
- Ask your technician to check drain-line heater amperage on freezers.
- Fix door leaks so less moisture enters the box.
Drain line design basics
- The line should slope continuously downhill from the pan.
- Inside a freezer, it needs a heater along its full length.
- Outside the box, a trap stops warm air being drawn into the box.
- It should discharge to an approved drain with an air gap where required.
- It should never rise or sag into a low spot inside the box.
Bay Area note
Many Bay Area cities require walk-in drains to discharge through an air gap to an approved drain, and inspectors check this on new installs. When we fix drain problems, we also check the discharge arrangement so the repair does not create a code issue.
What not to do
- Do not chip ice from the drain pan with metal tools; pans crack.
- Do not pour boiling water into a freezer drain.
- Do not block or cap the drain line outlet.
- Do not ignore a slow drip; it becomes an overflow.
Owner records for the technician
Note when water appears in relation to defrost, how much there is, whether the pan holds water or ice, and whether the problem started after cleaning or a cold snap.
When to call a technician
Call if water keeps returning, if the freezer drain pan is full of ice, or if ice is growing into the coil. Left alone, a frozen drain leads to an iced evaporator and a warm box.
Open 7 days, 8 AM to 5 PM, with emergency service until 9 PM. CA Lic. #776244.
Frequently asked questions
Why is my walk-in cooler leaking water on the floor?
Most often the evaporator drain line is clogged, so the drain pan overflows. A cracked pan or an out-of-level evaporator can do the same.
How do I unfreeze a walk-in freezer drain line?
A technician thaws it and, more importantly, replaces the failed drain-line heater. Without the heater, it will refreeze within hours or days.
Is water under the evaporator normal?
No. Water should run into the pan and out of the drain line. Any water on the floor means something is blocked or broken.
What causes slime in the drain pan?
Bacteria and mold growing in standing water. Regular cleaning and pan treatments keep it under control.
Can a clogged drain make the box warm?
In a freezer, yes: the water refreezes into the coil. In a cooler, mostly it causes water damage and odors.
How often should the drain line be cleaned?
At each maintenance visit, usually twice a year, more often in produce and floral boxes.
Can a drain pan be replaced?
Yes. Cracked pans are replaceable parts.
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