The issue is that the water hitbox is a 3x3 radius, instead of 1. This video shows the bug in Minecraft. --> https://1drv.ms/v/s!Aosj3tm3y-bsg_ImWxHBi4P6nd1_iw?e=wRGvhB

Steps to reproduce:

1. place a water bucket down, in any place

2. stay exactly a block outside of its reach

3. you will see that you can float in the air even though there isnt any water in the block area.