I think Shape Water is my favorite cantrip. Shape Water was one of four new elemental cantrips in the Elemental Evil Player’s Companion intended to give spellcasters some control over the elements. There is no doubt that Shape Water is the most versatile and powerful cantrip, but understanding why this is the case requires a bit of examination.
The following explanation may surprise you. We will look at the game rules obviously, but we will also need to consider physics, chemistry, and fluid dynamics to understand how water functions in the real world and how it can be incorporated into your game.
Introduction of Water?
My presence has probably already worn you out. The question “what is water. On its face, it seems so silly that even raising it seems pointless. However, having a clear answer that you and your DM both agree on is essential to how Shape Waterworks.
As an example, I have a cup of pure water. There’s no doubt about it. Next, I add a small amount of another liquid substance without water. The first few drops of water are still enough to say that I have a cup of water. After you pour your mystery liquid into your water, it will cease to be water at some point, and you will think of it more as a mixture or as a diluted quantity of that mystery liquid. Let’s say that instead of mystery liquid, you’re mixing dirt into water. When does it become mud and stop being muddy water? Even though jellyfish are 95% water, they are not “water.”
Water Physics (The Deep Analysis)
Water has simple physics at its core. Approximately 32 degrees Farenheight is the freezing point of water and 212 degrees Farenheight is the boiling point. There are differences depending on what’s dissolved in the water (salt, etc.) and pressure, but in general, that won’t matter much since measuring temperature doesn’t come up much in a game where dragons breathe fire.
The expansion/contraction that occurs when water or ice is transitioned to/from each other is when things get weird. Water expands when it solidifies, unlike most substances that shrink when they solidify and become denser. The crystalline structure of water ice is also the reason that water ice floats in the real world. Because of this, water ice is less dense than liquid water.
Shape of Water
Once we’ve discussed water and what it is, how big it can be, and how heavy it can be, let’s talk about some actual game mechanics. Let’s talk about Shape Water specifically. The spell isn’t in the SRD, so I can’t reproduce any significant portions of it, but you can look at it for free and beyond to follow along.
Shape Water targets water within 30 feet of you that fits within a 5-foot cube. Unfortunately, this is somewhat vague and does not specify if the shape of the area can be chosen. If we want to keep it simple, let’s assume that you can construct simple geometric shapes like cubes, spheres, pyramids, cones, and cylinders, but you cannot construct a ladder from ice by using water from a lake. Do not worry; we’ll figure out a way to violate the spirit of that agreement.
Bullet 1: Moving Water
The simplest Shape Water option is simply to move water 5 feet. There is a clause stating “any direction,” but this does not mean you can redirect it partially. It is technically impossible to use this effect to make water flow from one glass into another in a neat arc, but you might be able to move the water directly above the other glass and let gravity do the rest
It makes sense that the movement from this cannot cause damage. It’s not like a rushing river because you’re only moving water up to 5 feet over the course of 6 seconds.
Changing the flow of water is largely unexplained, and since this effect is instantaneous, it’s not completely clear what would happen if you were to use this feature to redirect a moving water source such as a stream of water spraying through a hole in the wall.
