Certified GKH Gardening Expert
Stick your finger into the soil after watering and make sure the water is actually penetrating the soil. Sometimes potting soil can dry out and start to repel water rather than absorb it. If you find this is the case, soak the whole thing in a tub for a half hour or so to force the soil to absorb the water.
Less likely but still possible is that the water is not draining out and the roots are drowning. Check to make sure that the plants are not in standing water.