A key technological challenge in constructing underground buildings and structures made of cast-in-situ reinforced concrete is the development of a reliable waterproofing system. The article highlights that construction joints being the most vulnerable areas of underground cast-in-situ structures require structural and technological solutions to ensure reliable waterproofing. Currently, there is insufficient emphasis on ensuring the technological reliability of waterproofing systems. Metal-sheet waterstops are used in waterproofing construction joints on domestic construction sites, in particular. However, existing structural and technological solutions often lack high technological reliability. The article identifies the main disadvantages of existing structural and technological solutions for waterproofing construction joints with metal-sheet waterstops, which reduce the overall technological reliability of the waterproofing system. Through a structural and functional analysis of the identified disadvantages and leveraging innovative technologies from industry, the authors propose a comprehensive set of new structural and technological solutions that allow eliminating the identified disadvantages and enhancing technological reliability of waterproofing construction joints in underground cast-in-situ structures. The novelty and practical applicability of some of these solutions proposed by the authors have been validated through Russian invention patents.