It's probably caused by leaf scorch. This happens when the weather is very hot and is made worst if it's windy. It doesn't matter how much water you give it as the leaves won't be able to take in moisture from the roots quick enough and the result is exactly what you have described.

You need to move the plant to a position that is preferably sheltered from the hot noon sun and out of the wind to stop this happening.

And. they're deciduous, so the leaves will be falling now anyway, so they should be fine next year. As M says, acers need a sheltered spot to really enjoy themselves, like us. The red one goes by the correct cultivar name 'Bloodgood', by the way, not the vampiristic nomen you gave it!