How much irrigation that is needed very much depends on where you are and what kind of tree. After the first few years it take to settle, trees have deep roots

How much irrigation that is needed very much depends on where you are and what kind of tree. After the first few years it take to settle, trees have deep roots and rarely need watering. And I have never heard of trees contribution negatively to "biological contaminants", whatever that means. Rather, trees contribute to a cleaner and healthier environment.