I would like to add two points to this discussion one is in response to "I've heard that it's bad for the tree too but you do see alot of people who do it." I must say that most of what I see people doing around trees is Not good, but as trees are long lived its quickly lost on humans that a tree that should last 300 years that only lives 40 years is a very sad state of affairs. Just because the tree "survives" while that homeowner resides there does not mean that they have been good caretakers of their trees.
"Some say Oak doesnt need much water, but the
flowers will........Not a good combo....." Oaks, are the species Quercus, and are found across north america, europe, and asia and are found in many different climates and environs. Living in California our Oaks have evolved to the dry summers and as such the most effective way to kill an Oak here is to water it in the summer. Now Oaks that have evolved in areas that receive a lot of summer rains would be a different story as to how they will respond to additional irrigation. One can not go wrong by looking at the natural conditions under which that tree species has evolved and try to as closely match that as possible in ones yard. Everyone go out and hug their tree!