If water is the key to life, how can excessive water intake be dangerous?

The human body is constantly maintained in a delicate equilibrium for optimal function.

The intricate organs and tissues preserving this stability have tremendous reserve to buffer changes from internal or external cause. Nonetheless, should the changes exceed the capacity for compensation then balance will be disrupted.
Overconsumption of pure water, especially if ingested in a short timeframe, can severely dilute the electrolytes in the body and result negative health outcomes.