"I apologize if this surprises you, but I do have a sense of decorum."

Whether or not he actually feels apologetic is not a question worth asking. He sniffs in disdain at Lan Sizhui's dismissive motions, instead seating himself by the edge of the pool and preparing to soak his feet in it.

This water is good for cultivation then, is it? That's what's being implied here? Well it's not like they'll be staying here forever, so he might as well! Take advantage! Of Sizhui's so courteously friendly invitation.