Watering citrus trees can sometimes be tricky. However, keeping a feel for the moisture level in the soil is one of the best ways you can gauge whether or not to water. Scratch just under the surface of the soil... If it is moist you should be good to go. What happens in many cases is that too much water is surrounding the trees for an extended amount of time and the roots become weak. Water effects in either direction, too much or too little, are never seen right away. What you will see is an after effect that creates chlorotic leaves and many times leaf drop. Keeping a consistent watering schedule is best if you can.
Symptoms of water needs are curling leaves. Muted color and leaf drop. Think of the leaf drop as a way for the tree to sustain itself through drought. If it drops leaves there is nothing to care for and it can put its hydration to where it is needed... Staying alive and holding out for the next watering
Too much water means muddy soil and citrus trees hate wet feet. They desire the moist/damp setting. That is why it is always recommended to use a well draining soil in citrus containers with holes in the bottom.