Hi Kev, I've got an old K reg Swift Kontiki which had the same prob recently. The water pump should not run when all the domestic water taps are turned off. Each tap, hot and cold supplies in kitchen and bathroom, has its own microswitch fitted below each tap, below the work surface. Access can easily be gained by removing the tap unit and lifting it free a couple of inches. In your case it is possible that one of the microswitches has become detached from its mounting, if so it would then be in a continually 'on' situation! Start with the kitchen taps, remove the four screws and carefully lift the unit and check below. Replacement taps are available from the 'Whale Elegance' range on the Leisureshopdirect web site. Good Luck.
Stewart
May 2010