A common reason why dishwashers leaks is using the wrong type of detergent. Only use automatic dishwasher detergent, and only use enough for your dishes. If you have soft water, use less detergent. Never use old detergent, as this can cause excessive sudsing, which causes water and suds to leak out of the base and sides of your dishwasher door.
Your dishwasher door has a seal that runs around it. If this seal gets torn or starts falling off, water leaks out around the door. Reattach the seal if it's not staying on the door. Order a new seal from a dishwasher parts dealer since it's difficult to fix the seal once it's broken. Verify that the door hinge and door latch are not broken. Replace these components, if necessary, since they are difficult to repair. If the tub is overfilling and spilling water onto the floor, see if the float switch is underneath the water or floating on it. If it is underwater, you need a new switch since it's difficult to repair.
Dishes/Main Tub Seal
Improper loading of your dishes can also cause leaks. Never place large pots and pans near the door of the dishwasher. Water bounces off of these items and through the door. Always load the lower rack with dishes to prevent the spray arm from directly spraying water onto the door. Water can squeeze through cracks in the gaskets and out of the base of the dishwasher. Never use water above 150 degrees Fahrenheit, since it can compromise the seals. Check the main tub seal, which is located underneath the impellers, spray arm and lower rack. If the seal is torn or cracked, order a new one.
Hoses/Water Inlet Valve
You have fill and drainage hoses on the back your dishwasher. If these hose connections aren't tight, you see water underneath your dishwasher. Tighten them, and clean out the hoses if they are clogged, which causes water backups. Replace or patch any hose that is split or cracked. Check the water inlet valve, and see if the rubber tube that runs along the center is punctured. Replace the hose. If the valve itself is leaking, you need to order a new one since it's difficult to repair this component.