DnD 5e - Practical Guide to Shape Water
Last Updated: October 2nd, 2020
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Shape Water may be my favorite cantrip. Introduced in the Elemental Evil Player's Companion, Shape Water was one of the four new elemental cantrips intended to offer spellcasters some magical control over the elements. Of the three cantrips, Shape Water is without question the most versatile and powerful, but understanding why that's the case requires some examination.
This article may take you to some unexpected places. We'll look at the game rules of course, but we'll also need to spend some time consider physics, chemistry, and some fluid dynamics to understand how water works in the real world in order to apply that knowledge in your game.
What is Water?
You're likely already tired of me. The question "what is water?" seems so silly on its face that the fact that I'm raising the question seems like a waste of time. But having a clear answer that you and your DM both agree upon is foundational to how Shape Water works.
For example: I have a cup of pure water. That's clearly water. I then stir in some quantity of another liquid substance that contains no water. The first few drops we can still say that I have a cup of water. As you pour your mystery liquid into your water, at some point it'll stop being "water" and you'll think of it more as a mixture or as a diluted quantity of that mystery liquid. Now imagine that your mystery liquid is instead dirt, and you're mixing it into water. At what point does it stop being muddy water and become mud? Jellyfish or 95% water, but they're not "water".
Defining a test for what constitutes water is hard. Purity is clearly part of it, but it's unclear how much. Here is what I propose to judge if a substance is water:
- The substance is a liquid composed primarily of water
- The substance's viscosity is consistent with water (it's not sludge, gel, etc.)
- The substance is not so full of other substances that a layperson would identify it as a different substance, such as blood, syrup, or wine.
That test rules out steam, ice, vapor, simple syrup (water super-saturated with sugar), poisons, alcohols, bodily fluids of most types, oil, and many "solutions" which players might try to argue are water due to their component parts. It also rules out plants, animals, and other creatures since a layperson wouldn't identify a jellyfish as water despite being composed of 95% water.
The basic physics of water are fairly simple. Water freezes at roughly 32 degrees Farenheight, and boils at roughly 212 degrees Farenheight. These numbers shift a bit based on what's dissolved in the water (salt, etc.) and pressure, but the vast majority of the time that won't really matter since measuring specific temperature doens't come up much in a game with dragons that breath fire.
Where things get weird is in the expansion/contraction in the transition from ice to water or from water to ice. Most substances get smaller when they solidify and become more dense, but water actually expands. This is responsible for all sorts of interesting erosion effects in the real world, and it's the reason that water ice floats: water ice is less dense than liquid water due to water ice's crystaline structure.
When water freezes, it expands by approximately 9%. So a 5-foot cube expands to be roughly 5 feet and 5 inches to a side, and its volume increases from 125 cubic feet to 136.25 cubic feet. The weight doesn't change, and spilling a few inches outside of a 5-foot cube likely won't have an effect in game terms.
Water Volume and Weight
Knowing how much water you need to fill a container can be very useful. It may surprise you to find out how much water it takes to fill a given space and how much all of that water weighs. It sounds tempting to haul around a bunch of water to power Shape Water, but you'll quickly find that doing so can be impractical, so you'll need to make do with small quantities in most cases.
Units of Measure and Converisons
A small selection of units of water which you're likely to encounter in a game of Dungeons and Dragons are assembled here for your reference. People who understand the metric system will likely find this list maddening, but Dungeons and Dragons uses Imperial measurements so we're all going to have to suffer through it together.
|Gallons||Sphere Diameter||Cube Size||Weight (Pounds)||Why did I list this?|
|1 Gallon||0.64 feet||6.14 inches||8.34 pounds||For converting gallons to pounds|
|3.92 Gallons||1 foot||9.67 inches||62.43 pounds||1-foot sphere|
|7.48 Gallons||1.22 feet||1 foot||62.43 pounds||1-foot cube|
|119.90 Gallons||3.12 feet||2.52 feet||1000 pounds||Maximum weight you can lift with Telekinesis|
|489.60 Gallons||5 feet||4.03 feet||4,083.26 pounds||Biggest sphere that you could make|
|935 Gallons||6.2 feet||5 feet||7,797.9 pounds||Biggest cube that you could make|
Common Containers of Water
Below is a small collection of containers in which you might commonly carry water. Combined with the conversion table above, this should give you an indication of how much water an adventurer could reasonably haul around.
|1 - Weight of contents; does not include container|
Now that we've looked at the absolute basics of water and what it is and how big and heavy it can be, let's talk about some actual game mechanics. Specifically, let's dig into Shape Water and how it works. Unfortunately the spell isn't included in the SRD so I can't reproduce the text in any significant portion, but you can see it for free on DnDBeyond so you can read along as we go.
Shape Water targets "an area of water" that fits within a 5-foot cube within 30 feet of you. This is somewhat imprecise, unfortunately, and doesn't specify if you can choose the shape of the area. To keep things simple, lets assume that you can use simple geometric shapes like cubes, spheres, pyramids, cones, and cylindars, but you couldn't do something like create a ladder out of ice by selecting some of the water in a lake. But don't worry, we'll find a way to break the spirit of that agreement.
Shape Water's first effect is instantaneous, but the other three effects can last for up to an hour. You can end those effects early with an Action or someone could dispel them, but otherwise the effects remain in place. You could be disintegrated and your 5-foot cube of ice would still be there taking up space for an hour. You can have no more than two ongoing effects at a time. It's not explicitly stated what happens if you try to create more, but in most cases with similar spells the oldest effect immediately ends. Your DM might instead decide that your attempt to create a new effect simply fails.
Bullet 1: Moving Water
Shape Water's most basic option is simply moving water 5 feet. It does specify "any direction", but that means that you can't redirect it part way. You technically can't use this effect to cause water to pour itself from one glass into another in a neat little arc, but you could move the water directly above the other glass and let gravity handle the rest.
The movement from this can't cause damage, which makes sense. You're moving a bunch of water 5 feet over the course of up to 6 seconds so it's not exactly a rushing river.
The option to change the flow of water is largely unexplained, and since this effect is instantaneous it's not at all clear what would happen if you try to use this to redirect the flow of a moving water source like a creek or a stream of water spraying through a hole in a wall.
There isn't a ton that you can do with this, but here are a few useful ideas:
- Move boiling water out of a pot and above someone you wish to harm
- Empty a fountain, pool, or other container
- Redirect the flow of water from a geyser, fountain, etc. momentarily
Bullet 2: Animating Water
This is likely the Shape Water option which sees the most use. If you have water, you have a malleable, pliable material with which to create simple shapes and animations. This is amusing and potentially very useful on its own, but the real appeal is what happens when you freeze the shapes you make.
Some examples of how you could use this:
- Create shapes such as signs to direct other creatures
- Communicate visually over long distances, such as by making the water into letters if you need to
- Power a waterwheel
- Move water between containers
- Position water in the shape of simple items like ladders, chairs, boxes
- Position water in the shape of simple structures like walls or small bridges
- Position water to serve as an obstacle by filling a space wholly or partially
Bullet 3: Color and Opacity
Easily overlooked, but potentially very useful. Changing the water's opacity means that you can turn murky, opaque water into water that you can easily see through, potentially revealing hidden stuff like treasure or lurking creatures. Changing the color of liquid is mostly for flavor, but a clever player might still be able to use it to good effect. Note that the wording says color or opactiy, so if you want both you need to use both of your ongoing effects.
Some examples of how you could use this:
- Change water's color and opacity to resemble wine to cheat in drinking contests
- Search murky water for objects or creatures
- Turn water opaque to hide objects or creatures, including yourself
Bullet 4: The One With Ice
This is where Shape Water gets crazy. The previous effects have been neat for flavor and occasional clever utility purposes, but the ability to instantly turn water into ice is incredibly powerful. Using bullet 2 and bullet 4 in conjunction allows you to build simple tools and structures out of ice, and you can even create large ice shapes and hit things with them. Even with a tiny amount of water you can get away with a lot of mischief.
Shape Water is silent on the durability of the magically-frozen ice, which I assume to mean that it's just normal ice for the most part. It can chip, break, melt, etc. during its 1-hour existence.
Some examples of how you could use this in conjunction with bullet 2:
- Freeze a door, a window, a gear, or another moving part to keep it from moving
- Freeze a water source at a choke point to block its flow
- Freeze water and give it to someone; unfreeze it to convey a pre-determined message like "we're in trouble"
- Freeze water in an open body of water to give you something to stand on
- Freeze water in the shape of a flat surface covered in spikes
- Freeze water inside a lock; the expanding water breaks the lock
- Freeze water into a sturdy shape to bridge part of a body of water
- Freeze water into the shape of a sphere then roll it down a hill
- Freeze water into the shape of a wall to give yourself cover
- Freeze water to damage or slow a ship
Where Do I Get All of This Water?
You have some options. A waterskin gives you enough water to mess with locks, to stop doors, to plug holes, etc.. A barrel contains enough water that you could produce tools like ladders or containers or other furniture-sized things. But that's not a bottomless supply. Some or all of your water will invesitably be spilled or evaporate. What we need is a truly endless supply of water.
Enter the Decanter of Endless Water. It can produce up to 30 gallons of water per turn, allowing you to produce all the water that you could need. Keep in mind that you need to spend an Action to open and activate it, so you can't do something like start it, drop it on the floor, and start shaping water while it gradually floods the carpet. Still, you can fill containers to accumulate water and gradually accumulate enough to make large shapes. If you don't have a convenient container, you can use Bullet 2 to shape one, then bullet 4 to freeze it. Repeatedly fill and resize the container until you have all of the water that you need.
Using Shape Water in Combat
Using Shape Water in combat is objectively hard. It is not intended to be a weapon. But "hard" is not "impossible". Unfortunately, we're beyond the explicit text of the rules at this point, so the rest of this article will require some imagination and cooperation from your DM.
If your DM gets unhappy about the options explored below, have a well-reasoned discussion with them. They want you to stop breaking the game with a cantrip that doesn't deal damage, and that's a perfectly reasonable thing to ask. Remember that we're all here to have fun, and you ruining the game by dopping 4-ton blocks of ice on all of your problems will stop being funny after the first few attempts. You might also remind your DM that situations where you can use Shape Water offensively either require a suitable environment (fighting beside a river) or a great deal of setup (rolling a heavy barrel around a dungeon).
Below are a handful of offensive use cases and an exploration of rules around them. Remember that your DM is the final arbiter of the rules, and they are within their rights to disagree with my suggestions. The damage suggested below makes use of the "Improvising Damage" section of the Dungeon Master's Guide and a handful of comparisons to items or spells which might work similarly.
The text of Shape Water makes no assertions about the state of the water being targeted except that it's water (and therefore not ice or vapor). Boiling water is still water, and hitting something with it is generally harmful. The complicated part is deciding how much damage it should deal.
Being burned by coals is listed in the Improvising Damage table as dealing 1d10 damage, stumbling into a vat of acid is listed as dealing 4d10, and being submerged in lava is listed as dealing 18d10 damage. Being struck with boiling water should be compared to those suggestions. Wikipedia lists the temperature of lava as generally between 1,292 and 2,192 degrees Farenheit. Water becomes steam long before that temperature, so 18d10 is out of the question. "Stumbling into a vat of acid" doesn't necessarily mean being submerged, and I honestly don't know if generic "acid" is more causting than boiling water.
I propose scaling damage based on the quantity of water used. You may not have enough water to exactly reach each of the steps I propose in the table, so either round or choose a number of damage dice which falls between steps.
The damage is probably fire damage, but I would also grant resistance to the damage to creatures made of water like water elementals. I would also grant a Dexterity save to halve or even negate the damage equal to the spellcaster's save DC.
Probably the simplest way to use Shape Water offensively, pour some water on the floor and us the bullet 2 to shape it into a flat sheet with protruding spikes, then freeze it with bullet 4.
How much damage to deal here is difficult. Ice is fragile, and generally when an icicle hurts someone is more because of its weight than the fact that it's pointed (though more weight behind a smaller point hurts more, which is why spears are a thing). So it's totally fair to say that ice spikes either couldn't cause piercing damage when stepped on.
Even so, I think the best comparison is to caltrops: a Dexterity saving throw to avoid them, and if the creature fails their stop moving this turn, take 1 damage, and have a 10 ft. speed penalty until they heal. I think making the floor spikes only work once then become difficult terrain seems like a perfectly find solution. If that still seems problematic, grant Advantage on the save to creatures wearing shoes.
The giant rolling stone is a classic trap. What if you could capture that same potential to crush stuff in the form of a 5-foot, 4-ton sphere of ice? Well, now you can, provided that you can get that much ice in place to animate it into a sphere and then get it moving fast enough to hurt something.
How much damage to deal is hard to answer. Dungeons and Dragons doesn't have a momentum to damage calculation. Being hit by falling rubble deals 4d10 and being crushed by compacting walls deals 10d10, so 10d10 seems like a good maximum and and 4d10 seems like a good minimum. The DM can adjust the damage within that range depending on the size of the sphere and how fast it's going.
Personally, I would say that the sphere needs to be moving at least 30 feet per round to deal damage, and I would allow a Dexterity save against a DC equal to the spellcaster's spell save DC to avoid the sphere. The DM might also allow a creature to perform a Strength (Athletics) check to stop the sphere.
The most obvious way to use Shape Water offensively is to drop something heavy on a creature. A 5-foot cube of ice weighs just under 7,200 pounds (according to aqua-calc.com). For comparison, a typical sedan weighs somwhere around 3500 pounds. Consider dropping two of them on top of someone without the advantage of "crumple sections". That would hurt.
Note that a 5-foot cube of water weighs roughly 7,800 pounds, but ice is less dense and therefore lighter for the same volume. It's not clear what happens to the water/ice which expands beyond the 5-foot cube affected by Shape Water, but let's assume that it returns to its natural state in order to keep things simple.
Again, we go back to the Improvising Damage table. Being hit by falling rubble deals 4d10, which seems low. Being hit by a crashing flying fortress deals 18d10, which seems high since a stone building would be heavier than our block of ice even at its maximum size of roughly 7,200 pounds. Being crushed by compacting walls deals 10d10, which seems like a fair amount of damage to use for our full-sized block of ice. But putting a 7,200 pound object above another creature is really hard, so we need some smaller sizes that we could reasonably move around, like a 1000-pound block which we could lift with telekinesis.
Assume that any of the example weights below have fallen at least 10 feet to gain momentum before striking a target. You might also add additional damage based on the distance fallen.
Damage dealt this way should be bludgeoning damage, and the creature should recieve a Dexterity saving throw to halve or avoid the damage against a save DC equal to your spellcasting DC. I don't know enough about ice to know how a block of ice would handle being dropped from various heights.