Is there a puddle in front of your dishwasher? Often this is a relatively easy problem to solve. At best, all you need to do is tighten a few fittings or level the dishwasher so water doesn't slosh out when the machine is running. At worst, you may need to replace a door gasket.
Remove the service panel that runs along the front of the dishwasher just below the door. If it is screwed in place, remove the screws with a screwdriver. If the panel hangs on hooks, pull the panel out and swing it up to remove it from the hooks.
Check the end of the drain hose that connects to the dishwasher. If it's leaking, tighten the clamp with a screwdriver.
Check the drain hose connection to the kitchen sink drain. Again, if it's leaking, tighten the clamp with a screwdriver.
Check for leaks around the water-inlet valve. If necessary, use an adjustable wrench to tighten the compression fitting that connects the water-supply line to the valve. If the fill hose is leaking, replace the spring clamp that is on the hose with a worm-drive hose clamp. It produces more clamping pressure. Use adjustable pliers to compress the spring clamp so you can pull the clamp and hose off the valve. Remove the spring clamp from the hose. Buy a worm-drive clamp at your hardware store, then install it and tighten it with a screwdriver.
Remove the front access panel (see step 1, "Tightening the fittings"). This will give you access to the dishwasher's adjustable feet.
Open the door completely and remove the bottom dish rack.
Unscrew the dishwasher from the kitchen countertop so the dishwasher can move freely as you adjust the feet.
Check to see if the dishwasher is level side to side. Place a small level inside the dishwasher so it's sitting on the bottom pan and facing parallel to the front lip of the dishwasher. If the dishwasher is not level, use adjustable pliers to turn one of the dishwasher's front feet up or down until you hit level.
Check to see if the dishwasher is level front to back. Turn the level perpendicular to the door, and place it on one of the bottom ledges that run along the side of the cabinet. Check the level again. If the dishwasher isn't level, use your adjustable pliers to turn the back feet up or down until you hit level.
Reattach the dishwasher to the countertop and reinstall the front access panel.
Inspect the door gasket. As it ages, the gasket can crack or become hard, preventing it from sealing completely.
If the gasket appears solid, adjust the door latch so the door seals tightly. Loosen the screw that holds the door latch to the cabinet. Push the latch in slightly and retighten the screw. Test the door and readjust the latch if necessary.
Replace the gasket if water continues to leak after you've tightened the latch. Most gaskets are held by compression in a groove on the door or on the dishwasher cabinet.
Pull the old gasket out of its groove, using adjustable pliers (see illustration). Take the gasket to an appliance store to get a replacement.
Soak the new gasket in warm water to soften it, then press it into the groove. Start at the top, then work your way down the sides and across the bottom.