How do I connect a dishwasher water supply line?

A dishwasher ties into your kitchen in three separate ways, and each one has its own rules.

• Hot water supply. Most dishwashers run on hot water, typically around 120°F at the tap. The supply is usually tapped off the hot side under the kitchen sink, often with a dual-outlet or tee shutoff that also feeds the faucet. The line ends at the dishwasher's inlet valve, a brass fitting at the front-bottom of the unit.
• A dedicated shutoff valve. The supply line should have its own shutoff valve so you can stop water to the dishwasher without killing the whole sink. This makes future repairs simple and is standard practice on a clean install.
• The drain path. The drain hose carries dirty water out. It must rise into a high loop secured under the counter, or connect to an air gap mounted on the sink deck, before it drops to the disposal or drain. This keeps wastewater from siphoning back into the clean dishwasher.
• Electrical. The unit needs power, either hard-wired or plugged into a dedicated outlet. New wiring is electrical work, not plumbing, and is regulated separately.

Pull the manual for your exact model before you start. Inlet thread sizes, hose lengths, and bracket positions vary by brand, and the manual is the final word on your unit.

The drain connection is where code matters most, because it protects your drinking water. Phoenix follows the Uniform Plumbing Code (UPC), which treats a dishwasher drain as an indirect waste that must be protected against backflow. The UPC states:

"No domestic dishwashing machine shall be directly connected to a drainage system or food waste disposer without the use of an approved dishwasher airgap fitting on the discharge side of the dishwashing machine."

An air gap is the small chrome or plastic cylinder you see poking up next to many kitchen faucets. The drain hose runs up to it, water passes through an open vertical space, then drops down a second hose to the disposal or drain. Because there is a physical break of air in the line, dirty drain water can never be sucked back into the dishwasher, even if the sewer line backs up.

Where local rules allow it, a high loop can serve the same purpose. The drain hose is strapped to the underside of the countertop as high as it will go, then routed back down to the connection. The loop sits above the flood level of the sink, so backflow has to climb higher than it ever will in normal use. The air gap is the surer method and the one the code language above points to, so confirm with your inspector which one your install needs. If you are adding or changing the drain, a permit may apply, so check before you cut.

For more on the device itself, see our page on what is a dishwasher air gap. If your existing unit drains poorly, see dishwasher not draining.

These are the core steps for connecting the water side of a standard under-counter dishwasher. Follow your model's manual for exact fittings and torque.

1. 1Shut off the water. Close the hot water shutoff under the sink. If there is no dedicated valve, close the main and plan to add one. Open the faucet to relieve pressure. Our guide on how to shut off water to a fixture covers this.
2. 2Cut the power. Switch off the breaker for the dishwasher circuit. Confirm it is dead before touching any wiring. Leave electrical rough-in to a licensed electrician if it is new.
3. 3Position the dishwasher. Slide the unit most of the way into the cabinet opening, leaving enough room to reach the front connections. Feed the supply line, drain hose, and power through the holes drilled into the side of the sink cabinet.
4. 4Connect the supply line. Attach the supply line to the dishwasher's inlet valve. Most units use a 90-degree brass elbow fitting threaded into the valve. Wrap the threads of the elbow with plumber's thread tape, then thread the supply line onto it. Hand-tighten, then snug with a wrench. Do not crank it down hard.
5. 5Add or connect the shutoff valve. Tie the other end of the supply line into the shutoff valve under the sink. If you are adding a valve to existing pipe, that is supply work that may need a permit.
6. 6Route the drain hose. Run the drain hose up to the air gap or into a high loop strapped high under the counter, then down to the disposal inlet or drain tailpiece. Secure all hose clamps.
7. 7Remove the disposal knockout plug if draining through a disposal. New disposals ship with a knockout plug sealing the dishwasher inlet on the side of the unit. If you connect the drain hose without removing it, no water can pass and the dishwasher will not drain. InSinkErator's installation guidance directs you to knock out that plug before connecting the hose: set the tip of a screwdriver against the plug inside the dishwasher inlet, tap it once or twice with a hammer to break it loose, then reach in and remove the loose plug so it cannot wash into the disposal and jam it. This is the single most common reason a freshly installed dishwasher will not drain. If you drain directly to the sink tailpiece instead, there is no knockout to deal with; you connect the drain hose to a branch tailpiece fitting.
8. 8Leak-test. Open the shutoff slowly. With the dishwasher still pulled out, watch the inlet valve and every joint. Run a short cycle and check again as water moves. Restore power only after the water side is dry.

Small details on the supply side decide whether the connection stays dry for years.

• Use thread tape on tapered pipe threads, not on compression or flare fittings. Wrap plumber's thread tape two or three times clockwise around the male threads of the inlet elbow. Compression and flare fittings seal on a surface, not the threads, so tape there does nothing useful.
• Hand-tight plus a quarter to half turn. Brass inlet fittings strip or crack if you overtighten. Snug them by hand, then add a short turn with a wrench. The manual gives the exact target for your model.
• Do not kink the supply line or drain hose. A sharp bend behind the unit restricts flow and stresses the fitting. Leave gentle loops.
• Test under real pressure. A joint can look dry until water actually flows. Run a full fill cycle and check again. Wipe each fitting with a dry paper towel and look for any dampness.
• Match the fitting to the valve. Inlet threads differ by brand. If the fitting does not start by hand, stop. Forcing the wrong thread will ruin the inlet valve.

A drip you catch on install day is a five-minute fix. The same drip behind the dishwasher for a month rots the cabinet floor.

Swapping a dishwasher into an existing, code-compliant hookup is a reasonable DIY job. The work crosses into licensed and permitted territory when you change the rough-in.

You should call a licensed plumber and check on a permit when the job involves a new water supply line, a new drain connection, or any change to the drain or supply rough-in behind the wall or under the floor. Cutting into existing pipe to add a shutoff or a branch drain is plumbing work that Phoenix may require a permit and inspection for. Any new electrical rough-in or a new circuit is a job for a licensed electrician, not a plumber, and is permitted separately.

A pro is also the right call if you find old, corroded shutoffs, a drain with no air gap or high loop, or signs of a past leak under the sink. Fixing those at install time costs far less than a water-damaged cabinet later. HQ Plumbing & Air handles dishwasher supply and drain hookups across metro Phoenix, including the air gap connection your inspector will look for.

Whatever route you take, follow your dishwasher's installation manual to the letter. The manual reflects the testing the manufacturer did on that exact model, and it overrides any general guide, including this one.