While plants tend to droop and wilt when dry, lawns don't do that. Here are 3 visual signs that your lawn needs some water: 

1) Leaf blades are folded in half lengthwise as they attempt to conserve moisture.

2) Footprints remain visible in the grass long after they'd been made. 

3) Grass appears bluish-gray rather than green before turning brown (a yellowing lawn is a sign of a different problem).