How do you simulate the warm water?

Oh, lol, now I get your question. Yea, it turns out the silence and lack of distractions are what produce "shower thoughts", more so than the act of showering itself.

Doing any relatively rote act like washing dishes, walking places, etc can also give rise to them. Not having a device in your hand to constantly steal your attention really helps though.

Play it on a speaker.

With a faucet my good friend!