Hello Duncan,
You describe the water as having a foul taste. This could be down to two common causes that have been described many times in this forum.
If the water tastes of TCP, then it is the hose/pipe work which is imparting the taste to the water flowing through it. Solution is to have all the pipe work replaced.
If the water is brackish - musty etc, then it is almost certainly the pipe work which has become infested with a mould. If the infestation is relatively new, then it can be possible to flush it out using proprietary cleaners such as Puri-tabs, Hydrogen peroxide, or Chempro-SDP always follow the instructions on the packets for dilution soaking times and final flushing.
Sadly if the infestation has been in place for some time, the 'roots' of the spoors can become ingrained in the interior walls of the pipe work, and will not be fully removed by flushing. Again the solution is total pipe work replacement.