Jerry,
On my last rig my water pump refused to pump after storing it dry for a few cold winter months. I went straight to the nearest RV store, bought a pump, replaced it and all was good.
Curious about why the old one quit, I took it apart. It looked fine. I put it back together, hooked it to a spare battery and it ran perfect. Internet reading suggest there was a small piece of something in it that interfered with the pumping diaphragm.
I now have a spare for me or anyone I'm camped next to that has a failure!