What did the Hittites mean by the sun god in the water?

In the context of Hittite religion, the "sun god in the water" was a specific manifestation of the male sun god, known in Hittite as Istanu. Hittite theologians likely used this designation to refer to the sun as it appeared reflected in the waters of a lake.1

This deity was distinct from the sun goddess of Arinna, who served as the patroness of the Hittite state. While the sun god was associated with this aquatic reflection, official theology also recognized a sun god or goddess of the underworld, representing the sun's journey through the netherworld during the night.1