Is the water pump failing or the tap-switch?
There's a simple trick to test if it's the water pump that fails, or if it is a broken microswitch in the tap:
Go under the sink, find the tiny connectors that connect the tap leads to the battery (they are usually wrapped in a piece of folded isolation plastic, tucked away behind the sink).
Detach the two connectors. Take the right hand connector (usually with two brown leads that go out of the cabinet to the battery).
Bow a paperclip to form a plug (see picture), and push the two ends into the two holes of the connector. By shortening these 12 Volt + and - wires, you imitate the microswitch in the tap.
If you hear the pump working and water is flushing from the tap, you know two things for sure: pump is o.k. and fuse of the pump is o.k.
Third thing you know now, is that there is something wrong with the microswitch in the tap.
This is a nice trick if you a) can't open the lid of the water tank (like me), and b) you don't carry a multimeter around on holidays (like me).
Two things more: if you are able to get the microswitch going again (after cleaning it or sanding it), this usually works for only a short period. Better to change the tap. (We are on our third tap in the mean time).
And: if the fuse of the pump is blown, get a new pump. A blown fuse indicates trouble with the pump.
Aqueous regards from Amsterdam,
Marc.