To dream about seeing or being in a bathtub indicates a need for self-rejuvenation and liberation from daily troubles. You should lighten the load that you have been shouldering. It's also a sign that you crave affection, enjoyment and peace.
To dream that you or another person drowns in a bathtub shows that you aren't fully prepared to confront frightening things. You feel submerged in your subsurface thoughts. You should relax and slow the pace instead of plunging into things.