Water needs in your orchard will vary depending on the weather, the age and size of your trees, the time of year, and the soil type. Knowing how much to water, and when, is an important management consideration, and deciding how you plan to water will inform your planting and set-up choices.
eXtension.org provides a great overview of water's effect in the orchard: http://articles.extension.org/pages/60228/effect-of-water-on-apple-trees:-not-enough-or-too-much
