Water in thoroughly when planting. For bare root trees, you won't need to water regularly going forward, only water in dry spells when needed. You should be able tell because the leaves will start to wilt and droop. If a container grown tree, it will need more watering until its roots are established. It should be watered every other day or so for the first few months. Then reduce to twice a week until autumn. In the second year it should have a established enough root system to support itself, just water when required as explained above for bare roots. When watering a tree it is important to give a good soaking. It is better to water heavy and less frequently than little and often as this encourages the roots to grow down into the ground.

Don't worry, this isn't a hungry plant so your food bills won't be going up!