lads water in tanks happens in all garages .. most small older stations use dip rods to measure there fuel levels which will not let you know if theres water in the tank .. Bigger stations and properly run places with have veeder root guages which work on two magnetic floats , product float and a water float .. with 21mm of water in a tank an alarm will sound on the console in the shop .. water in taks can occur because of old age and even in the tankers themselves due to sea water .
advise the garage in question to get there tank dipped for water by there service company such as the company i work for because they might not have a guage . this is the worst news any station can get because it can ruin business.