If we refer to the gravitational action on the human body, actually, being in the water it is like being in space. In space, the gravitational action of the earth on our body is very small, due to the distance, for this reason it is that bodies can float in space. When we are on earth, the gravitational action is higher and is reflected as our weight.
According to the principle of Archimedes, when we walked into a liquid such as water, this exerts a buoyant force in the direction opposite to our weight; so that the resultant force that we received, is below than our weight, then we have the feeling that the gravitational force has declined as if we were in space. This fact is exploited to train astronauts in the work to be performed in space.