Running water can be a cause of problems, not least on the roads. A highway authority may find that water is prone to run on to the carriageway from adjacent land, especially in a hilly area. The adjacent land may not have proper drainage. Or its drainage system may not be properly maintained. Or there may simply be too much water flowing on to and across the land for its drains to cope. The result may be anything from a trickle to a torrent of water running on to and across the highway. What steps may a highway authority then be obliged to take?