Maybe since it’s water inflation try having all the water at the bottom of the body to make it more realistic

Well actually the person is lying flat down on the ground. Not standing up.

Well I would start off the feeling of cold (or hot water) rushing through the character's mouth as they gulp it down to where their bellies start filling up. The description I would use is that how soft and wobbly it feells, like a water balloon. And since it's water, it makes it much heavier so describe how the character felt weak to hold their water filling belly and fall to the ground. If you want, you can make the character huff and groan for how big (size of a beanbag chair) it is.

Hmmm. So the bigger they get, the heavier they feel as their belly fills up and expands. And I bet it would feel much like a water balloon. And add some sounds of pleasure in there too huh?

Of course, feeling pleasured to be swollen and very bloated will work. Unless you feel like it's not appropriate for a type of story you are going with, maybe muffling sounds or groans will do.

can never go wrong with a water attack inflating them from the inside, and of course theirs always the hose

Well the character definittly gets filled up with a hose.

With water inflation, it helps to describe how the water itself obeys gravity within the body,
Flowing towards the lowest point and spreading outwards from there, adding jiggle and squish as it steadily rises- until, at a point, when the water reaches all the way to the top, the backflow causes the entire body to rapidly tighten, swelling outwards more evenly rather than from the bottom upwards! Growing less blubbery, and more heavy and tight- at least, usually! Sometimes the soft, plush, squishiness can last to colossal sizes, depending on personal preference!
Another thing to remember is how water will sway and shake with movement- taking a step to the right will cause the water to SLLORMSH to the right as well, visibly tugging the person in that direction from the pendulum effect of all that weight being swung! Not just for the body, but for other parts as well!
Cheeks might bounce and bobble against the face, the fingers or toes might refuse to close anymore, the tail may even be rendered immobile, a big round waterball that can’t budge!
All sorts of different mechanics are possible with such a fluid!