water drainage system a cavern 10 with ceiling 12 and walls 14 16 is shown schematically a water draining pipe 18 hereafter called ceiling draining pipe made of plastic or metal is secured to the ceiling 12 with the help of a number of rock bolts 20 that are secured by being drilled into the ceiling the water is led downwards to the draining pipe via a canvas a tunnel canvas 22 which is stretched from down in the pipe and sidelong up to the rock wall ceiling 14 12 to which it has been fixed a second corresponding canvas 24 is stretched from the other side of the draining pipe and up to the other rock wall ceiling 16 12 and similarly fixed to the rock wall the lower end of each of the bolts 20 comprises a threaded section for screwing on one or two nuts 30 32 a number of such rock bolts see fig2 are arranged with mutual distance in a row along the ceiling to secure the ceiling draining pipe 18 the ceiling draining pipe 18 is led up towards the ceiling so that each bolt 20 passes through appropriate holes in the bottom of the draining pipe each sealing draining pipe is secured to the row of bolts at a correct slope with the help of the nuts see fig2 and 3 the sealing against water leaks through the holes in the draining pipe bottom is provided with the help of upper and lower gasket washer discs 26 28 the draining pipe is arranged with a given slope so that the water 51 may flow down through an opening 50 in the bottom of the draining pipe 18 and into.