The figure below shows the two main families of acetylcholine receptors: muscarinic and nicotinic. In structural terms, muscarinic receptors are G-coupled protein receptors, while nicotinic receptors are ligand-gated ion channels. They can be found on both sides of the synaptic cleft (presynaptic and postsynaptic).
After the pressure drops below 40 psi, the electrical switch turns on the pump and the pressure in the tank increases. Any failure in any component or loss of electricity can cause a well to suddenly stop producing water when a faucet is turned on.
As you can see, water intoxication and death from drinking too much water depends on the speed with which you drink it. You can drink the 1.6 gallons of water slowly over 24 hours without getting any water intoxication symptoms. However, if you drink it within an hour, you can die from water intoxication.