By the third week of July the lawns along the Whippany River side of town go pale and thirsty, and the ones that don't have a reason. NextGen Irrigation Inc. installs and repairs the systems behind that difference — zones laid to the shape of the yard, heads set level with the turf, controllers timed for the hour just before dawn when nothing is lost to the heat. A rain sensor saves a week of pointless watering; a changed nozzle erases a brown ring nobody could explain. Start-ups in spring and winterizing in fall bookend the year, air pushed through the lines ahead of the freeze. The reward is plain enough: green in August, on a street where green in August takes some doing.