Water arrives from the cold
You were born too warm and close to the star to keep much water of your own. So the water came to you, carried in on icy comets and damp asteroids flung from the outer dark, and breathed out by your own volcanoes. Steam thickened into an atmosphere, the sky cooled, and the rain began.
The first oceans
It rained for ages, and the water gathered in your low places until you wore seas. Now an impact that once left a scar just splashed and closed over. You had become a blue world, wrapped in air and water, sitting in the narrow band around your star where liquid water can last. The habitable zone.