You mean, hot or cold water line? Hot indeed. Although many (most) dishwashers have heating elements inside, it will always be more efficient for your 40Gal+ house water heater to supply the amount of hot water needed for cleaning a load of dishes.
Here's what Whirlpool says about the water hookup in one of their installation manuals:
You must have: ✓ a hot water line with 20-120 psi (138-827 kPa) water  pressure. ✓ 120°F (49°C) water at dishwasher. ✓ 3/8" O.D. copper tubing with compression fitting or        flexible stainless steel braided fill line(1/2" minimum        plastic tubing is optional but not recommended). ✓ a 90° elbow with 3/8" N.P.T external pipe threads on one end.
Do not solder within 6" (15.2 cm) from water inlet valve.