Dishwasher leaks are sneaky. By the time you notice water on the kitchen floor, it's often been leaking inside the cabinet for weeks. Here's what actually goes wrong with dishwasher hookups and how to prevent it.
The Three Connections That Matter
A dishwasher has three plumbing connections, and every leak we've ever fixed traces back to one of them:
- Water supply line — usually a 3/8" braided stainless line from the hot water shutoff valve under the sink
- Drain hose — runs from the dishwasher to the garbage disposal or sink drain tailpiece
- The dishwasher's own internal seals — door gasket, pump seals, float switch
The Drain Hose: Cause of Most Leaks
The number one issue is the drain hose loop. Dishwasher drain hoses must loop up high under the countertop before connecting to the drain — this is called a high loop, and it prevents dirty sink water from flowing backward into the dishwasher.
What goes wrong:
- The hose sags or was never looped high enough, causing slow drainage and backflow
- The hose connects to the disposal without the knockout plug being removed (on new disposals, there's a plastic plug inside the dishwasher inlet that must be punched out — miss this and the dishwasher won't drain at all)
- The hose clamp loosens over time from vibration
If your dishwasher isn't draining, check the knockout plug first. It's the most common cause on new installations.
The Supply Line
Use a braided stainless steel supply line, not plastic. Plastic lines crack. We've replaced enough of them to say this with confidence.
The shutoff valve under the sink should be a quarter-turn ball valve, not an old multi-turn gate valve. If your shutoff is seized or dripping, replace it when the dishwasher goes in — it's a 15-minute job while everything is already disconnected.
Air Gap vs. High Loop
Ontario plumbing code allows either a high loop or an air gap for dishwasher drainage. An air gap is the small chrome cylinder on the back corner of some sinks. Most Barrie installations use the high loop method, which is simpler and code-compliant when done correctly.
When to Call a Plumber
- You're replacing a dishwasher and the old shutoff valves are seized
- The drain connection doesn't match (older homes sometimes have unusual setups)
- Water is appearing under the dishwasher and you can't find the source
- The dishwasher was installed by a big-box delivery crew and something isn't right (we fix a lot of these)
A proper dishwasher hookup takes about an hour. A flooded kitchen cabinet takes a lot longer to fix.
Concepts Plumbing — Barrie, Ontario. Dishwasher giving you trouble? We'll sort out the hookup properly. Free Estimates. Honest Solutions. (705) 715-1513.
