Abstract: A flexible sealing layer (1) is provided for the collection and lateral drainage of existing water, especially in tunnel constructions. This sealing layer comprises unidirectional, continuously extending webs (3) arranged so that they project toward the water-permeable substrate, thus preserving the required space (D) for water drainage between the layer (1), in close contact with the substrate, and the substrate (U) proper. The webs (3) are of an arrow-like configuration (3') at the end projecting from the sealing layer. The sealing layer is fixed in place by locking or hooking the webs of the sealing layer into complementarily fashioned webs (7, 7') of fixing elements (4), which latter have been previously attached to the substrate (U) by means of nails (5), for example. This type of seal proves to be advantageous, in particular, if the tunnel tube is curved.