The USDA has some rules of thumb, green thumb, I suppose when it comes to watering your lawns and gardens

  1. One deep watering is much better than watering several times lightly.
  2. Lawns need about 1 inch of water each week. If the weather is very hot, apply an inch of water about every 3 days.
  3. Watering to a depth of 4-6 inches encourages deeper, healthier root development. It allows longer periods between watering.
  4. To measure the water, put an empty tuna can (or cat food can) on the lawn while watering. Stop watering when the can is full or if you notice water running off the lawn.