A water tank made of stainless steel and having a substantially cylindrical shape is provided. The water tank comprises curved stainless steel panels forming a cylindrical body of the water tank, fan-shaped stainless steel panels forming a cone-shaped top part and a cone-shaped bottom part of the water tank, packing members being inserted between connecting portions of the stainless steel panels, reinforcing members, each having an L-shaped cross-section, which are arranged on both side of the connecting portions, bolts and nuts for coupling the stainless steel panels and the reinforcing members together by being inserted into holes formed thereon, reinforcing bars, an air vent disposed on the center portion of the top part, and a drain pipe disposed on the center portion of the bottom part.