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How do spells like Control Water, Shape Water, and Create or Destroy Water (and possibly others?) work with water in pipes (let's say about a foot in diameter if that matters)?

Consider two cases:

  • enclosed pipes in which the water flows
  • a pipe that is open on one end and the water flows out of that end and falls on the floor

In both cases I will assume that the supply of water is virtually unlimited.

  1. Can the spells change the direction of the flow?
  2. Can they stop the water from flowing?
  3. Does destroying the water have any effect since new water will immediately fill the space?
  4. Can they (in the latter case) only affect the water that is already out of the pipe or also that which still is in the pipe?

I assume there will be an issue with my ability to see the water (at least in the first case) but what if I drill a small hole into the pipe?
Or what if it's made of glass?
What if I am in Border Ethereal?

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    \$\begingroup\$ for simplicity: the pipe might be made from crystal by another spell, making it visible \$\endgroup\$
    – Trish
    Feb 17 at 11:01
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    \$\begingroup\$ It is for just this reason that the Romans sensibly made their pipes out of lead; to prevent magic from affecting the water within. \$\endgroup\$
    – Kirt
    Feb 17 at 17:33
  • \$\begingroup\$ @Kirt so casting "poison Water" needs to be done at the cistern or lift the roof of an Aquaeduct. \$\endgroup\$
    – Trish
    Feb 17 at 17:35

1 Answer 1

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They don't

The rules do not describe a specific "water controlling spells" category, so we have to analyze spells on a case-to-case basis, along with the most generic rule.

By default, spells do not work without clear line of sight. Therefore, a solid pipe blocks spells, regardless of the construction material. Moreover, mentioned spells assume an open body of water, although the description varies:

These two facts suggest that mentioned spells aren't supposed to work in pipes.

The Standard Caveat: D&D 5th edition empowers the DM in ways that 3rd, 3.5, and 4th did not. While rule zero has always applied, 5th edition chooses not to explicitly codify many things. If your DM says the spell works, it works. As a player, you can always try to cast the spell and see what happens, or ask the DM if the character knows the expected result.

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    \$\begingroup\$ Thank you! I'm not sure I understand why water in pipes doesn't fulfill those definitions though. Can you please elaborate on your thought process there? I added my reasoning to the question since it wouldn't fit a comment length limit. Thanks! \$\endgroup\$
    – geckon
    Feb 17 at 15:14
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    \$\begingroup\$ @geckon are you a player or a DM? \$\endgroup\$
    – enkryptor
    Feb 17 at 15:49
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    \$\begingroup\$ As a DM, you're in control. You decide, how magic works in your games. If you think it is reasonable that Create or Destroy Water can destroy water in pipes, it definitely can. The rules give a huge leeway for out-of-combat magic applications. The developers say this is intentional. \$\endgroup\$
    – enkryptor
    Feb 17 at 16:11
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    \$\begingroup\$ @geckon this site specifically forbids asking for opinions. Rules, objective arguments and arguments based on actual experience are OK. But "what would be the effects of allowing spells to control water in pipes and other enclosed spaces?" would be a separate question. \$\endgroup\$
    – Mołot
    Feb 17 at 18:27
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    \$\begingroup\$ @geckon it's not the same question. This one ask how they work and the answer is they don't. If you want to know what would happen if you would allow them to work, then it's different question. This site is Q&A, not a forum, and asking followup questions is allowed, even encouraged. \$\endgroup\$
    – Mołot
    Feb 17 at 21:21

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