The Water-logged Note is a diary entry that can be collected in Metro Exodus.
Location[]
Volga: When you go to rescue Anna inside of the toxic bunker, go through the right doorway right after you fall inside. Go down the hallway and take another right. You will see a locked door. Break the lock and enter. The note should be on the crate next to the bed.
Transcript[]
...What are they even thinking just bringing all this shit here? It's got to be disposed of properly! Fucking crooks at disposal, splitting the funds with the generals, while we get to park our asses on decades-old shit... I wonder if it gets worse or better when it expires? And which would be better for us? The barrels sure look like they could start leaking any moment now... Will need to requisition a spare protective suit...