Dishwasher Not Draining: Standing Water and What Causes It
What's actually happening
A dishwasher drains into the same plumbing as your sink, usually through the garbage disposal or an air gap on the counter. That shared path is why this symptom so often has nothing to do with the dishwasher itself — a disposal full of scraps, a plugged air gap or a blocked sink drain will leave water in the machine while every part of it works perfectly. Work outward from the machine: filter first, then the connection, then the pump.
Check these first — they're free
- Run the garbage disposal for thirty seconds. If the dishwasher shares the disposal, anything sitting in it blocks the dishwasher too. Run it with water, then start a drain cycle on the dishwasher and see whether the standing water goes.
- Twist out the filter and clean the sump. Scoop the standing water out with a cup first, then lift the filter assembly. Rinse it under a tap, and check the well underneath for glass, seeds and paper labels — feel carefully, broken glass hides there.
- Pop the cap off the air gap. The chrome cylinder on the counter lifts and unscrews. Debris packed in the chamber is common in homes with a disposal, and clearing it takes two minutes.
What causes it, most likely first
Filter and sump packed with debris (most common, you can fix this yourself)
The cylindrical filter in the floor of the tub catches food, labels off jars, and broken glass. When it packs, water cannot reach the pump intake. Most modern dishwashers have a filter that twists out by hand and is meant to be rinsed monthly. It is the first thing to check and the most common single cause.
Garbage disposal knockout plug never removed (common, you can fix this yourself)
New disposals ship with a plastic plug sealing the dishwasher inlet, and it has to be knocked out during installation. When it is missed, the dishwasher has literally nowhere to drain from day one. If the machine has never drained properly since a new disposal was fitted, this is almost certainly it.
Blocked air gap or high loop (common, you can fix this yourself)
The small chrome cylinder on the counter beside the faucet is an air gap, and it clogs with the same debris the drain carries. Where there is no air gap, the drain hose should loop up under the counter before descending. A missing or dropped loop lets sink water siphon back and lets the machine drain poorly.
Drain pump failed or obstructed (common)
Under the sump sits a small pump. Glass fragments and fruit stickers are its usual enemies — they jam the impeller. A pump that hums without moving water is obstructed; a silent one has failed. Reaching it means removing the lower spray arm and sump housing, and on many models pulling the machine out from under the counter.
Kinked drain hose behind the machine (less common, you can fix this yourself)
Dishwashers get pushed back hard during installation or after a repair, and the drain hose gets crushed against the wall or a pipe. Nothing has failed; the water simply has no path. This is the check that saves a service call when the trouble started right after work was done in the kitchen.
When to call a technician
Call when the filter, disposal and air gap are all clear and water still stands after a cycle. That points at the drain pump, the drain solenoid, or a control that is not calling for the drain step at all — each of which means getting under the sump or into the door electronics. It is also the right call if you find glass in the sump, because fragments that reached the pump usually mean the impeller has taken damage too.
How long can it wait? Standing water goes stagnant quickly and will start to smell within a day, and a dishwasher that cannot drain also cannot run its next cycle. It is not damaging anything as long as it is not overflowing, but the cleanup is unpleasant enough that it is worth handling promptly.
What it costs
If you fix it yourself: $0 — filter, disposal, air gap and hose checks are all free.
Professional repair: A fixed price after diagnosis, agreed before any work starts; the diagnostic fee is applied to the repair when you approve it.
Frequently asked questions
Is it safe to run the dishwasher with water sitting in the bottom?
A small amount of water in the sump is normal by design — it keeps the seals wet. Several inches standing after a completed cycle is not. Running it again on top of undrained water usually just adds more, and if it overflows onto the floor you have a second problem.
It drains a bit but leaves water behind. Same causes?
Yes, at an earlier stage: a partly-clogged filter, a partially blocked air gap, or a pump losing capacity. Partial draining is the warning stage and the cheapest time to sort it out.
Could my sink being slow be related?
Very likely, if they share the drain. A restricted sink line backs up into the dishwasher's path. When both are slow, the plumbing is the problem rather than the appliance — worth knowing before you pay to have the dishwasher looked at.
How often should I clean the dishwasher filter?
Monthly for a household running it most days. It takes under five minutes, and it prevents both the drainage problems here and the poor cleaning results that come from recirculating dirty water.
Codes your machine may be showing
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