I went to Warwick to do the quest that allows you to add them as a settlement. The problem is, the settlement leader and two others are stuck inside of one of the water treatment containers and are underwater!!!

I've tried restarting and reloading previous saves. Any suggestions???

Go home.

Wait at least 72 hours.

Come back.

Site may have reset?

Thanks - I'll give it a try

It worked - thanks!

Do the cities reset/recycle periodically?

Yes. Game cells (areas) tend to reset after 73 in-game hours of not visiting them.

This happens quite a lot. In my second playthrough, the guy who was supposed to later figure-out Warwick is a synth drowned in there, right next to me. The number of settlers dropped from 6 to 5.