It's often tricky to distinguish the two. Typically, under watering will cause brown, brittle leaves while overwatering will result in soft, yellow leaves. It's important to note that the symptoms for overwatering are similar to not supplying enough light, and the symptoms of underwatering are similar to not supplying enough light.OverwateringIf you believe you overwatered your plant, first check the bottom of your planter for drainage. If there none to little drainage there are two options:Let your plant dry out and transfer it to a planter with ample drainage.Drill drainage holes in the bottom of the existing planer, if possible.Underwatering:If you believe you underwatered your plant, you should immediately water the plant. Additionally, you should consider shortening the time between waterings, and/or begin watering your plant more throughly.