A New Water Manifestation

The last few months have seen a new water based phenomenon. A short burst of water will pour from a tap that is firmly turned off. This originally started about a year ago and was quite amusing as I blamed our farms old water supply. When on holiday the other week near Glastonbury the water in our caravan did the same thing, and it was on mains. Again the tap was turned fully off. Starting to get a bit worried now. Finally on returning to my house in the village, the tap there is now doing the same thing, and it has just had a new washer fitted. This is not coincidence...