Universal adapter for water connections, adapted to allow a correct and quick installation of any connection of a water system, wherein the universal adapter consists of a box profile having a front face, a rear face, an upper face, a lower face; said box profile at the front face being provided with a larger slot (6.a), with height of between 21 mm and 40 mm, preferably 32 mm and length of between 1⁄2 and 3⁄4 of the total length of said box profile, preferably a length equal to 2/3 of the total length of the box profile; said rear face being provided with a smaller slot (7.a) coaxial with said larger slot (6.a) and of smaller height, of between 11 mm and 32 mm, preferably 21 mm; said box profile being further laterally provided, both on said front face and on said rear face, with at least one pair of fixing holes (4-4'); said box profile being further provided, at said front face, with at least one pair of levels (5-5'), in particular a horizontal level and a vertical level arranged respectively on the left and on the right of the larger slot (6.a) or vice versa; said rear face being provided with at least one pair of viewing holes (16-16'), coaxial with said levels (5-5'), adapted to allow the operator to view said levels (5-5') also from the other side of the box profile; said universal adapter being suitable for water connection being implemented according to the following steps: first alignment step; in said first alignment step, said box profile being arranged with a preselected point of said smaller slot (7.a) at a female connector of the water connection to be implemented; said preselected point being determined from the technical installation specifications of the fixture to be connected to said water connection; in said first alignment step, a common male plug being inserted into the larger slot (6.a) in the point coaxial with the position of said female connector, until the threaded projection of said male plug reaches said female connector and is screwed by an operator therein; at the end of said first alignment step all the female connectors of said water system being stably connected and aligned with said box profile and with the respective male plugs; said first fixing step being repeated for each water connection to be implemented until the space available in said larger and smaller slots (6.a-7.a) of said box profile is completely used; second fixing step; in said second fixing step, an operator, through said fixing holes (4-4'), fixes said box profile to the wall, selecting the optimal position with the aid of said levels (5 -5'); third closing step; in said third closing step, said operator completes the finishing steps for the wall involved with the water connection; fourth disassembly and finish step; in said fourth disassembly and finish step, said operator disconnects all the male plugs from the relative female connectors, now fixed in the wall and perfectly flush with the wall; said operator proceeding with the disconnection of said box profile from the wall and carrying out the final operations for finishing the wall. first alignment step; in said first alignment step, said box profile being arranged with a preselected point of said smaller slot (7.a) at a female connector of the water connection to be implemented; said preselected point being determined from the technical installation specifications of the fixture to be connected to said water connection; in said first alignment step, a common male plug being inserted into the larger slot (6.a) in the point coaxial with the position of said female connector, until the threaded projection of said male plug reaches said female connector and is screwed by an operator therein; at the end of said first alignment step all the female connectors of said water system being stably connected and aligned with said box profile and with the respective male plugs; said first fixing step being repeated for each water connection to be implemented until the space available in said larger and smaller slots (6.a-7.a) of said box profile is completely used; second fixing step; in said second fixing step, an operator, through said fixing holes (4-4'), fixes said box profile to the wall, selecting the optimal position with the aid of said levels (5 -5'); third closing step; in said third closing step, said operator completes the finishing steps for the wall involved with the water connection; fourth disassembly and finish step; in said fourth disassembly and finish step, said operator disconnects all the male plugs from the relative female connectors, now fixed in the wall and perfectly flush with the wall; said operator proceeding with the disconnection of said box profile from the wall and carrying out the final operations for finishing the wall.