Remote water pump switch - latching relay?

Tom_M wrote:
Another type of latching relay uses a single coil and magnet. The first pulse pulls the contacts in and the magnet holds them in place. To release the contacts you pulse the coil with a reversed polarity pulse.

This is the principal used in most RV battery disconnect relays. Actually, the magnet pulls a swinging lever in place to block the opening of the contacts. When the reverse polarity pulse is applied, the magnetic field swings the lever out of the way and the contacts are allowed to open. Very simple and very reliable. No holding current required. They would require a bit of sophistication on the switch arrangement to accomplish the pulse polarity reversal.