Water stops are necessarily used in construction joints to prevent water from
passing through concrete joints which leads to avoid corrosion in steel bars.
[http://1.bp.blogspot.com/-6aRtMi97vp4/VRStbbcEGjI/AAAAAAAABsk/XNeRdq8dOdo/s1600/download.jpg]

In some cases, it is required to weld/overlap two or more water stoppers like in
wall junctions.

[http://2.bp.blogspot.com/-7ycDGcm92v4/VRStobWIS0I/AAAAAAAABss/v9LMraF3Nz0/s1600/images-1.jpg]

Types, sizes, colours, etc. are varying from supplier to another.