Lora, the grasses vary widely in their water needs, but if you have 'normal' warm season growers like Miscanthus and Pennisetum, grasses that get big in the summer before blooming, you probably don't need to water them until you see obvious signs that they need it.

An exception would be those that haven't been in the ground for at least 2 years. Younger plants need more attention. Just like us!

since they are newer you prolly should water them some.

normally they will do okay without water... but then watering helps them grow bigger and stay nicer looking, or in other words they are low care plants that will still benefit from being pampered