Water Plane

From Manuel of the Planes (3e):

It is an ocean without a surface.

It is domain of current and wave.

It is a bottomless depth.

The Elemental Plane of Water is a sea without a floor or a surface, an entirely fluid environment lit by a diffuse glow. It is one of the more hospitable of the Inner Planes once a traveler gets past the problem of breathing the local medium.

The eternal oceans of this plane vary between ice cold and boiling hot, between saline and fresh. They are perpetually in motion, wracked by currents and tides. The plane’s permanent settlements form around bits of flotsam and jetsam suspended within this endless liquid. Even these settlements drift on the tides of the Elemental Plane of Water.

The Elemental Plane of Water holds but one great immediate danger, and that is the fluid nature of the plane itself. Unless a traveler can breathe water or has no need to breathe, any visit to the Elemental Plane of Water must be  brief. Those unable to breathe must hold their breath while on the plane and run the risk of drowning, as detailed in The Drowning Rule in Chapter 3 of the Dungeon Master's Guide.

Creatures made of fire (such as fire elementals) take 1d10 points of damage each round on the Elemental Plane of Water, because it has the water-dominant trait. Creatures with the fire subtype are very uncomfortable on the plane.

A great difference between the Elemental Plane of Water and other watery domains is a lack of pressure. In Material Plane oceans (and some others), the pressure of the water increases with depth. The water pressure can grow strong enough on the Material Plane to crush the life out of creatures and bend steel. But the pressure on the Elemental Plane of Water is no worse than a just few feet underwater in a Material Plane ocean, so there are no dire consequences.

Long-term survival on the Elemental Plane of Water is fairly easy. Obtaining water is obviously not a problem, though its purity and salinity may pose some difficulties in specific areas. The abundance of sea life in the plane is enough to satisfy any traveler with a taste for fish.

A vague, dim glow that issues from all sides illuminates the seas of the Elemental Plane of Water. This glow gives everything a blue-green aura, but limits clear vision. Normal vision, including darkvision, is limited to 60 feet. Clouds of silt, algae, and other detritus may limit sight even further.