terrainWater

The material a terrain field's water surface draws with — lakes, rivers, the sea, and the skirt that carries the sea past the field's rect.

It is a plain transparent PBR body of water with no simulation behind it, which is what makes it correct at every scale the surface is used at: a pond, a river reach and a horizon all read the same. terrainSystem.spawn applies it to a terrain's water entity unless waterMaterial names another.

It draws in the transparent queue after the terrain, with both faces, so the ground under the surface is already in the frame and the same material is the underside once the camera goes below the waterline.

Reach for @builtin::systems.oceans instead when the water is the subject — that package simulates a spectrum, whitecaps and shore foam, and wants an ocean rather than a terrain's water table.