Many years it is not necessary to water your lawn in the spring due to the abundance of rain. During the summer months your lawn needs 1 to 1.5 inches per week. If at all possible only water the lawn between 4:00am and 9:00am to prevent the lawn from developing a fungus. Watering after an application will not harm the effects. Rain will not effect the results of your lawn application. An easy way to test the soil is to do a moisture test by taking a knife or screw driver and inserting it into your soil about 2 to 3 inches. This should be fairly easy in a well watered lawn.
Mowing
Fescue should be mowed between 3 to 4 inches to help shade the root system and retain water in the soil. Try not to mow no more than 1/3 of the blade off.
Bermuda should be mowed at 1.5 to 2.5 inches during the growing season.
Zoysia should also be mowed at 1.5 to 2.5 inches during the growing season.