* Speak with Miageau. He will tell you he needs water from the Sacred Cheval River. He instructs you to buy a Blessed Waterskin from the other friar (to your right, by the bottom of the stairs). Trade 10g to Nouveil to buy the waterskin, then head to East Ronfaure.
* Trade the waterskin to the targetable "Cheval River" area (in place of a ???) at (H-5) at the start of the river to receive the Cheval Water.
* Return and trade the Cheval Water to Miageau for your reward.