Symptoms for both under-watering and over-watering are wilted and scorched leaves. Both conditions can prevent tree roots from effectively transporting water to the top of the tree and that tree will express these symptoms. In addition, too much tree water can also shut down sufficient oxygen to the roots. Some tree species can handle "wet feet" but many trees can not.
How To Water A Tree
Supplemental watering during drought conditions can prevent tree decline, pest problems, and non-recoverable tree root and canopy damage. Young trees planted in the landscape and certain drought prone species need regular watering during dry periods.
Depending upon soil texture, density of water competing plants, daily temperatures, and rainfall amounts, 1-3 inches of water per week should keep a tree healthy. Trees should be watered once or twice a week in the growing season if there has been no significant rainfall. A few heavy (high volume) waterings are much better than many light, shallow waterings and all trees need to be properly mulched.
Don't Over Water A Tree!
As I have mentioned, if the leaves are wilting or scorching and you have faithfully been watering, you need to check if there actually is too much water for the tree. The best way to check for wet soil is to dig down 6-8 inches and feel the soil. The soil should be cool and slightly moist but not soaking wet.
You should be able to press most non-sandy soils into a ball and it stay together. If the soil ball falls apart, then the soil may not have sufficient moisture.
If the ball you just made will not crumble when rubbed, you either have a clay soil or the soil is too wet to crumble when rubbed. This is an indication of too much water, so watering should be stopped. Sand and Clay soils are not a good tree growing medium in the landscape although many species have naturally adapted to these soils. Sandy soils are doughty and clay soils mimic wet soils.