Hi leon, young plants don't need lot of water, just keep the soil a little wet, watering early in the morning and/or in the evening, up to me i prefer not on the leaves.
At the plant growing and tale place, water quantity can be 10 to 100 liters per day, if you watering all the plant (main vine and secondery vines), it depends how hot, the number or leaves, but in general, pumpkins are drunkers !! LOL
When the fruit is pollinated, nice watering can begin and at the end of fruit growth you must slow your watering system.
Stéphane (hope it help a little !)