The crystals of the title new melaminium salt, 2,4,6-triamino-1,3,5-triazin-1-ium acetate acetic acid solvate monohydrate, C(3)H(7)N(6)(+).CH(3)COO(-).CH(3)COOH.H(2)O, are built up from singly protonated melaminium residues, acetate anions, and acetic acid and water molecules. The melaminium residues are interconnected by N-H...N hydrogen bonds to form chains along the [010] direction. These chains of melaminium residues form stacks aligned along the a axis. The acetic acid molecules interact with the acetate anions via the H atom of their carboxylic acid groups and, together with the water molecules, form layers that are parallel to the (001) plane. The oppositely charged moieties interact via multiple N-H...O hydrogen bonds that stabilize a pseudo-two-dimensional stacking structure.