and the water relaxes you, makes the process much easier. it can feel as if your body is a part of the water. it can be difficult to know where your physical body ends and the water begins.
meditation can be very intense. you are completely alone with your thoughts. no distractions. no avoiding them. many people find that their thoughts are calmer and that they have a strong peace of mind, once they settle into the tank and the feel of the water.
you become in tune with your true nature, your core self. your deep-seated emotions are easier to access, along with it being more straight-forward to release any blocks 