1. I’ve noticed that you and your parents have been fighting a lot these days. I would like to help calm the troubled waters if I can.
2. Mr. Williamson has been someone that we could depend on for strength and comfort ever since our father died. He has been a bridge over troubled waters.

The expression uses the metaphor of rough (troubled) water and is frequently accompanied by related vocabulary such as “to calm or to pour oil on,” “bridge over,” “deep in,” “wading into,” etc.