Each soil type and grass species differs in its water needs. 

To be reliably successfu, your watering program should factor in soil type, grass species, rainfall, and evapotranspiration. 

For example, sand soils require more water than clay soils as the water is not retained as well. Also remember, compost will increase the soil's capacity to retain water for longer periods of time.

Species such as buffalo grass, fescues, Bahia grass and centipede grass require less water than bluegrass or Bermuda grass. 

Keeping in mind your local rainfall is also important. In times of increased rainfall, your yard will not need as much additional water.