In high summer, lawns need about 1 1/2 inches of water a week (shrubbery and garden beds require 2 to 2 1/2 inches) to stay green and healthy. Gauging how quickly a sprinkler delivers the right amount is easy. Set an empty, regular-size coffee can about 10 feet away from the sprinkler (or closer, if 10 feet is outside the watering zone). Turn on the tap, and monitor the time needed for the sprinkler to deposit enough water to reach 1 1/2 inches on a ruler dipped into the can. Next time, you'll know just how long to run the sprinkler.
Homemade Water Gauge
Martha Stewart Living, March 2001