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First determine your lawn watering needs:
Evapotranspiration is the easiest way to determine if you are over or under watering your lawn.
Evapotranspiration, measured in inches or millimeters, is the amount of water that evaporates from the soil plus the amount of water that transpires through the leaves of a specific plant, in this case, lawn grass.
The following instructions will help you use evapotranspiration information to prepare a lawn-watering schedule for your lawn.
Steps to take:

1. Set five flat-bottom cans or coffee mugs at various places on your lawn. Try to place them halfway between the sprinklers or in areas that generally receive the least water. More than five cans may be necessary for large lawns.
2. Turn on your sprinkler system for exactly 15 minutes.
3. Measure the depth of water in each can and determine the average water depth of the five cans.
4. Check the chart below for the water depth in inches according to the season.
5. Read the number of minutes you should water about every second or third day and record the times for future reference.

Table 1. Watering schedule based on average water depth

Number of minutes to water twice weekly:
Average water depth in cans (inches) after 15 minutes	Spring	Summer	Fall
1/8	66	115	46
1/5	44	77	30
1/4	33	57	23
1/3	26	46	18
3/8	22	38	15
1/2	16	28	11
5/8	13	23	9
3/4	11	19	7
1	8	14	5
1 1/4	6	11	4
1 1/2	5	9	3

Additional water-saving tips

• Best watering times are early morning.
• Adjust to the guide recommendations for naturally occurring precipitation.
• Watch for visual signs of under-watering such as dry spots or wilting.
• If water is flowing off the grass into the gutter, divide the watering time into two blocks to allow the soil to accept the applied water.
• Increase the amount of water over the spring season to reach the summer water needs, and gradually decrease the amount of water in the fall as the winter rains approach.
• Reduce watering times by 20 percent of the time suggested in the guide if you have a Bermuda grass lawn or another type of low water-using grass.
• Water slightly more for small lawns surrounded by concrete or other heat-reflecting urban structures.

I hope that you find this information useful and as always Happy Gardening.  If you have any additional questions don't hesitate to ask.