- Poseidon Reservoir safe key - Inside, next to a tool case behind a large pipe in the upper west section corner. Drop down from the catwalk above to reach it. Opens the safe in room behind the security doors and the tool case right next to the key.
The Poseidon Reservoir appears only in Fallout 4.
- Fallout 4 Vault Dweller's Survival Guide, page 354 - "Poseidon Energy Reservoir not only distributed water to the surrounding farmlands and towns, but it was also a source of hydroelectric power. The power generated was used by Poseidon for its research facilities scattered about the Commonwealth."