The biggest problem with groundwater, particularly in the sort of mixed soils that characterise much of the southern half of the UK, is how difficult it is to determine where it is in the ground. This, of course is not really what the client wants to hear.
You arrive on site with detailed plans of the buried services. The electricity and telecommunications can be readily confirmed with your Cable Avoidance Tool (CAT); the route of the gas main, sewer and water main are visually located through pavement scarring and covers.