Leaks in the water pump, heater core, or engine freeze plugs can also allow coolant to escape. (mechanics.stackexchange.com)
Freeze plugs are about the size of a US half - dollar (little over an 1»), and can come loose over time. (mechanics.stackexchange.com)
If there is water visibly leaking from an engine, there are a few major culprits: hose connections, the water pump, and freeze plugs. (mechanics.stackexchange.com)