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I was wondering if a person could use water breathing to avoid breathing a toxic atmosphere.

The spell itself states:

This spell grants up to ten willing creatures you can see within range the ability to breathe underwater until the spell ends. Affected creatures also retain their normal mode of respiration.

How does water breathing physically affect the target?

For example: When entering a dungeon which was sealed long enough so that there is nothing but CO2, the adventurers figure that out and enchant themselves with the water breathing spell. Could they expect to survive by breathing their full waterskins?

I'm hoping for a strict analysis of the RAW, if possible.

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    \$\begingroup\$ Reminder: comments are for clarifying content, not discussion. Please take any discussion to Role-playing Games Chat. Prior discussion has been removed. \$\endgroup\$ – SevenSidedDie Jun 15 '16 at 16:50

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Ultimately this is an edge case for a DM to adjudicate for their table. So I'm going to address the most likely interpretations and the argument for each. RAW, the spell grants "ability to breathe underwater until the spell ends".

A strict interpretation No, breathing your waterskin won't work. You are not "underwater". In the scenario posed above, this will likely keep the characters out of the dungeon. Not fun.

A loose interpretation Yes, the intent of the spell is to allow you to breathe water. Your water skins will work, but only about as long as a bag of air would in a similar situation. I.e.: one extra breath. In the scenario posed above, this will give the characters more time to look around but still keep them out. Still not fun.

A fun interpretation Yes, they can breathe out of the water skins for as long as the spell's duration. It magically grants you the ability to breathe water, and is not concerned about the physics of the question. In the scenario posed above, this will allow the characters to enter the dungeon, and require them to keep one hand occupied with managing the water skin. If they lose it, they must share or they are in mortal danger. This is a creative use of a spell and heightens the difficulty and excitement of the situation, making this particular dungeon delve a unique and memorable experience.

I know which one I'd choose.

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I personally feel that trying to understand how magic works in a scientific manner is making a category error: like trying to use microbiology to explain why my dog rolls over when I tell him to.

The spell does what it says it does:

... the ability to breathe underwater until the spell ends. Affected creatures also retain their normal mode of respiration.

The only question to answer is therefore does sticking your face in your water at count as being underwater?

This is an easy question: if the DM feels it should then it does, if not, it doesn't.

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  • \$\begingroup\$ Reminder: comments are for clarifying content, not discussion or argument. Please take any discussion to Role-playing Games Chat. Prior discussion has been removed. \$\endgroup\$ – SevenSidedDie Jun 15 '16 at 17:25
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My interpretation is that your lungs can also act as gills, so you are amphibious. This means you can also breathe water, but the water does not have unlimited amount of oxygen.

For instance, if you put a fish in a water bowl it will suffocate, because you need to replenish the oxygen in the water. (Ask a fish owner.) Thus, if you try to breath from a water bowl, the oxygen in the bowl will deplete quickly and you will suffocate.

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Contrary to Dale M's answer, I propose that the GM can (in the absence of rules governing the spell) invent a scientific background behind the spell that is consistent with RAW. If no scientific mode of action of the spell is specified in the RAW, it can be based on keithcurtis' answer as the GM deems fit.

In order to let the players explore the dungeon like reverse diving bell spiders, the GM may (for example) rule that the spell works by the magical electrolysis of water to produce oxygen.

Having a more accurate model of how the world works makes the players more likely to be convinced by the GM's actions, since they are based on in-world reasoning instead of mere GM rulings. This will also reduce the likelihood of arguments due to disagreements on GM rulings based on fiat.

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Firstly, whether or not water breathing is magical enough to effectively 'make' oxygen where there is none is debateable. Other answers have tried to deal with that fact, mostly concluding that it's up to you. The premise of this answer is that water breathing only allows you to breathe oxygen that is already in the water. It attempts to calculate how long a human could survive on just the oxygen dissolved in the average waterskin.

DISCLAIMER: This is just my attempt at a calculation; if you spot any errors, and there probably will be at least one, please do tell me.


The PHB says that a waterskin holds 4 pints of liquid (probably fresh water). 4 pints is about 2.3L. Assuming that the temperature is about 20°C (just above room temperature), fresh water can hold a maximum of 10mg/L dissolved oxygen (using this data about sea and fresh water).

Our waterskin therefore holds, assuming the 'best-case scenario', about 23mg dissolved oxygen. 23mg is 0.023g

An adult needs about 840g oxygen per day (according to NASA). That's 35g per hour, 0.58g per minute, or 0.01g per second. Based on these calculations, an adult could breathe in sufficient oxygen for 2.3 seconds from the waterskin before running out.

Using the suffocation rules in the PHB (pg. 183), and assuming that the character has a CON of 14, they could hold their breath for 3 minutes, then could last 12 seconds (two rounds) before dropping to 0hp.

Using this method, a character could expect to stay conscious for 3 minutes and 14.3 seconds before dropping. After that, by the rules, the character could become stable through death saving throws.

In reality, the results would be more serious (see this source). After 15 minutes, recovery becomes virtually impossible as too many brain cells have died.


Your character is therefore likely to survive 18 minutes and 14.3 seconds before being so deprived of oxygen that they might as well be dead. Not a particularly effective strategy all things considered...

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I would say maybe..

All depends on interpretation how the spell actually work. If water breathing allows you to breath water trough skin, then you can use it only when your entire body is covered by water. Hence your idea wont work.

If from other hand spell gives your lungs ability to extract oxygen from water, then you should be able to breath with your water from waterskin.

Looking at the description of spell in source material, reference website or offical manual on p 191:

This spell grants up to ten willing creatures you can see within range the ability to breathe underwater until the spell ends.

I would suggest it is more likely targeted creature absorbs air from surrounding water and not from inhaling it to lungs. But again, I would say let your GM decide how this spell actually work.

But... even if it work, it will not be infinite. Look, there is no infinite amount oxygen in water, and if you put fish in closed container for too long it might suffocate. Your idea with using waterskin would work similar if you wont't cast any spell, and instead filling it with water, fill it with air.

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I'd say it's open to interpretation. The spell says "breathe underwater", not "breathe water" and that's pretty much where interpretation starts.

If I was to adjudicate this as a GM, I'd allow it, as long as your head is fully inside the water container. Unless the water skin is transparent, this effectively means you're blinded for the duration. Probably good enough to get you out of the room, probably not useful for a full crawl of the dungeon.

It probably also means pouring the water from the water skin, into another water-proof bag, as water skins frequently have an opening that is too small to fit the head of a typical adventurer through.

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I alway interpreted this spell as : "Your lungs now behave as gills when you're breathing underwater."

Which mean that you can extract dioxygen dissolved both in the water and in the air.

So your plan to explore the dungeon seems ok. Though i'm not sure how the players are going to keep their heads into the water, but that's another issue.

(also, H2O running out of O doesn't exist: in pure H2O there is alway twice as many hydrogen atoms than oxygen atoms)

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    \$\begingroup\$ From a chemical point of view, the water remains unaltered as it is prosessed by the gills. The oxygen collected by the gills is dissolved in the water, not the oxygen atom that's a part of the water molecules. So the water becomes poorer in dissolved oxygen over time (eventually killing any fish in it of oxygen deprivation), but remains water (H2O). \$\endgroup\$ – kviiri Jun 14 '16 at 11:36
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The gas that you breath in and out from the air and from the water are the same. Your water container will mix its soluble gas with those present in the air, and any excess of CO and CO2, or deficit of O2, will stay a problem regardless.

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  • \$\begingroup\$ This answer seems to be a frame challenge--one that contests the premise of the question. Please see the linked meta for good advice on how to construct such answers. \$\endgroup\$ – nitsua60 Jun 16 '16 at 14:44
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I doubt there's specific rules-as-written specifying the difference here. I would say the intent of the spell is that you can breathe water like everything else that can breathe water -- ie. needing to have oxygen in it. But there's nothing to say it doesn't let you breathe water regardless.

Can you replace the CO2 with a poisonous gas that doesn't necessarily dissolve in water? That way, this time, the water-breathing trick will work (you can always say "it's a good idea and you don't know for sure, you should try it").

But it allows you to deny in other situations (eg. lets go in space, we have infinite "air", lets bypass the enemy's breath weapon) if that seems more appropriate.

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