Exact meaning of this water sign
The sign indicates that the water supply valve (Wasseranschlussventil - AV) is located 0.5 meters to the left and 17.0 meters in front of the sign.

This Wikipedia page has all the details, though it is in German. But maybe Google translate will help if you're not fluent enough to read it.


  
  Designation in abbreviation of the installation fitting.
  Inner diameter in millimeters of the supply line.
  Distance between shield and installation fitting measured from the plate to the left . This is given in meters (field 3 and left) and
  decimetres (field right, after the comma).
  Distance between shield and mounting fitting measured from the shield to the right . This is given in meters (field 4 and left of it)
  and decimetres (field right, after the comma).
  Distance between shield and mounting fitting measured straight away from the shield . This is given in meters (field 5 and left) and
  decimetres (field right, after the comma).