In most cases if a plant is getting too much water it can drop its leaves.  The same thing happens when it does not get enough water .  The difference is that when it is over watered the leaves are soft and limp.

Under watering makes the leaves are crispy and brittle.  Remember if you over water you will kill you plants just as fast as if you don't give them enough water.

Keep in mind when planning your garden to group like plants together.  Plants that have different watering needs will not thrive in the same area.  Different parts of your property have different soil types and require and appropriate water levels.