Your lawn needs 1 to 1-1/2″ (3-4cm) of water weekly. Mother nature provides water, but she sometimes needs help. To determine the need for supplemental water, look for these telltale signs of oncoming drought stress:
Areas of the lawn especially near concrete or asphalt (sidewalks and driveways), under large trees and on slopes, take on a dark, silvery or smoky blue-green haze. In extreme cases the lawn appears yellowish.
Footprints or lawnmower wheel marks don’t spring back shortly after they are made.
If your lawn shows symptoms of drought, water it immediately regardless of the time of day. Under normal circumstances, early morning is the best time to water your lawn so that the leaves can dry slowly and naturally without too much evaporation and instead with most of the water penetrating the soil. Regular, fairly deep watering is better than daily light sprinklings. Deep watering and allowing the lawn to dry out between watering will force the roots to penetrate deeper in search of moisture.