Twenty-five to 50 percent of the water you spray into the air will evaporate. Watering during the heat of the day also stresses plants due to temperature changes. Late evening and early morning are the best times to water. Lawns and shrubs should be watered thoroughly once or twice a week, as opposed to shallow waterings every day. Shallow watering promotes a shallow root system, which causes the plant to suffer during dry conditions.
Rain gauges are available at most stores and garden shops, and are relatively inexpensive.
In lieu of a rain gauge, use a tin can to catch rainwater or sprinkler water and measure the depth with a ruler. Soaker hoses are better for watering shrubs, since they can be placed at the base of the plant to thoroughly water the root system. Less water is lost to evaporation, since it is not sprayed into the air.