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As water guns today can send a jet of water quite a distance away, I wonder how useful would a gun be, that sends an electric current over a jet of water to its target?

By useful I mean:

  1. Gotta be able to replace/complement standard small arms, in terms of range, firepower, others. I'm actually looking to have my protagonist be surprised by the devastation that this thing ought to wreck.
  2. Gotta be safe for the user. Some of the bad guys will get fried while testing it, but eventually I want it to be an evil horror weapon of the future, so safety first.
  3. Gonna need a cool name. All I got right now is hydralectrogun, suggestions for something better are most welcome :-)

I'm no expert on electricity but I realize that the hydralectrogun will be limited by the power output (power source), and by the range (water jet stability, delivery of the electric charge).

Whatdoyousay?

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    $\begingroup$ I know my answer sort of blew this out of the water (pun intended), but.. Watt-er gun, anyone? $\endgroup$ – Joe Bloggs Nov 2 '15 at 16:31
  • $\begingroup$ Not exactly the same, but related: worldbuilding.stackexchange.com/questions/17498/… Most of the problems pointed out in the answers to that question can be applied here. $\endgroup$ – Aify Nov 2 '15 at 16:48
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It will be less useful, more destructive, or less portable than you'd expect.

Firstly: Range. One of the big problems with water as a projectile is that it doesn't like sticking together when moving through the air. The easiest way to see this is to pour a bucket of water off the top of a tall building, you'll see that it very quickly disperses into a series of drops, rather than one cohesive lump. The reason for this is that the turbulence caused by the air rushing past the water is enough to break the surface tension of the water, except for small droplets. For your gun to have any decent range, it's going to have to push that water out fast, and as you're spraying it fast the leading edge of the stream is going to break into thousands of water droplets, rather than one cohesive stream. Why is this a problem?

Electricity doesn't jump as easily as you might think. While part of the stream might be capable of transmitting a current, most of the beam is going to be made of small droplets. From the point of view of the electrical current that's pretty much the same as a lot of air. You can get around this by pumping up the current voltage (Thanks Michael) enough for it to bridge from one drop to the next, but at that point it will also have enough oomph to bridge down all the other drops that are spraying down towards the ground (thanks to the aforementioned turbulence) and ground far short of the target. Or possibly to wrap back around to the operator and ground through him.

We can fix this by spraying more water to keep the stream continuous, but then we reach a different problem: Volume. The further you want an uninterrupted beam of water, the more water you have to push through at a high enough velocity to hit the target. This (sadly) means we have to spray water at an awfully high rate for an awfully long time, which equates to an awful lot of water. It goes from the portable to needing a van quite quickly...

The biggest problem, however, is establishing a potential difference to actually make the electricity flow. You can't set up a circuit through the gun because you'd need two (non touching) streams of water. You can't ground the power, because that would need your gun to be at potential the entire time, which is a very good way for your operator to get zapped and not a good way to deliver a life threatening jolt of power (without the aforementioned operator zappage).

Finally: Water is a great conductor of electricity. So much so in fact that if your enemy gets wet (because you just shot him with a water gun) most of the electricity would likely route down him and hit the ground without causing any damage whatsoever. And really, who wants a dread weapon that can be defeated with a pac-a-mac?

All things considered: You'd be better off with a Taser strapped to the bottom of a super soaker. The super soaker doesn't actually do anything useful, but at least it looks cool.

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    $\begingroup$ Wouldn't you need to raise the voltage, not the current, in the paragraph about electricity jumping? $\endgroup$ – a CVn Nov 2 '15 at 14:30
  • $\begingroup$ Indeed you would! Thanks for pointing that out! $\endgroup$ – Joe Bloggs Nov 2 '15 at 15:07
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    $\begingroup$ There's a Mythbusters episode where they attempt to address essentially the same question but in the context of urinating on the electrified third rail. They found that the urine stream broke up before it could reach the rail to conduct any current back to the poor sap too drunk to know where he's peeing. $\endgroup$ – Green Nov 2 '15 at 18:23
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    $\begingroup$ @Green : I'm guessing the OP has access to more powerful pumping technology than your average human urethra is capable of handling, so I explained further than just saying 'watch mythbusters'. $\endgroup$ – Joe Bloggs Nov 3 '15 at 9:26
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    $\begingroup$ «who wants a dread weapon that can be defeated with a pac-a-mac?.» I have no idea what that means. $\endgroup$ – JDługosz Oct 3 '16 at 17:40
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Not useful at all.

http://mythbustersresults.com/water-stun-gun

Myth busted.

Update because some people don't like answers that short.

If you have ever seen a stream of water under a strobe light, you see that what appears to be a continuous stream is actually a lot of separate droplets. That means that the electricity would have to travel many air gaps, which it does not do well. In practical terms, what appears like it should work would not work at all.

The Myth Busters team tried building a water-stream stun gun, and could not get one to work. It was not until they put 1 million Volts of electricity behind the gun that they managed to get it to work. However, a Tesla coil capable of generating 1 million Volts is not portable and would be impractical.

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Why use water?

Water is messy, short ranged, and would have a high chance of electrocuting the shooter.
If you're close enough to use a water gun, you might as well just use a taser and be done with it.

Instead of water, use an ionizing laser beam to create a plasma channel, and send the electricity down that.

This is real world, present/near future technology that's being developed by DARPA, and will probably be available on the battlefields in the next decade.

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  • $\begingroup$ This kind of taser? $\endgroup$ – Samuel Nov 2 '15 at 23:06
  • $\begingroup$ hmm, seems like everything that's worth doing has already been thought of... Yeah, I might go with that $\endgroup$ – Nahshon paz Nov 3 '15 at 8:32
  • $\begingroup$ @Nahshonpaz It's very rare to come up with an idea that no one has thought of before, at least in part. So do what everyone else does and take an existing concept and make it better. Take Samuels example for instance. He took the existing, real LIPC technology, and came up with ideas to improve on it. They may or may not work in real life applications, but you wouldn't know unless you actually built and tried one. Or, you can come up with something crazy that won't work with our current understanding, and you you might inspire future scientists to make it work, like Star Trek keeps doing. $\endgroup$ – AndyD273 Nov 3 '15 at 14:38
  • $\begingroup$ @Samuel Yes, you had a good answer, and it's a neat idea. Though I wonder, if you used it outside, could air currents cause the plasma to expand out of the channels, shrinking your 10 cm gap and cause a short circuit? I don't know how long the plasma stays ionized once it leaves the beam. $\endgroup$ – AndyD273 Nov 3 '15 at 14:44
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    $\begingroup$ @AndyD273 The voltage won't ever drop below 327 volts in air unless the two ionized channels completely touch each other (this is due to Paschen's law). If the taser is then limited 300 volts, quite enough to provide a large current to a human, the two channels will never arc between unless they somehow touch. But in either case, 300V or 10,000V, the entire blast happens so quickly (microseconds) that shifting air currents are not an issue. $\endgroup$ – Samuel Nov 4 '15 at 16:51
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Mythbusters did it: Mythbusters Water Stun Gun

In short:

  • You need a continuous, "laminar" stream of water. The electricity won't reliably arc through droplets at voltages that will stun but not kill. That meant the only production water pistol that worked was the largest one, one of the big syringe-type guns you use in swimming pools.
  • You need two streams, one for each side of the circuit. The earth isn't very electrically conductive; you need thousands of watts of power to reliably stream electricity using the actual "ground" as part of the circuit. That means the rig the Mythbusters came up with required two impractically large water cannons.
  • You need salt water. Potable drinking water like you get from your sink is actually a fairly poor conductor of electricity; its main shock hazard is that in small amounts it removes air gaps and increases surface area contact between you and a voltage source (and the salt on your skin will make a small amount of water more saline). To get electricity to actually flow through water, you need an isotonic (roughly body chemistry) or hypertonic (seawater) saline solution.
  • Distance is still a factor. Wires are used in modern tasers because the resistance over the 20-30 feet of wire is negligible. Even with electrically-conductive salt water, voltage is inversely proportional to the square of distance; at normal taser range, what you get through a stream of water from an ordinary taser is not enough to disable a human, and upping the voltage at the source makes it dangerous at closer ranges.
  • Any leak in the device, or even wet hands, and the shooter is in greater danger than the target.
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I don't know if this is helpful or not but the weapon would be better used in a non-lethal ship to ship capacity. Water is actually a poor conductor of electricity. It is the impurities in the water that make it conduct. Sea water would be a much better conductor and a ship could just have a hose in the water and one pointed at the target. As mentioned, the flow would have to be laminar, but with a nuclear powered warship at you disposal, maybe something could be done. You'd have to want to make it uncomfortable or possibly lethal for people on the other ship, but I'm not certain why you wouldn't just shoot them with bullets, you know the old way.

Also, you might consider some kind of futuristic coagulant that starts out low viscosity, so it flows through the gun and plumbing at greater velocity and then sort of adheres once it's airborne to hold the stream together. Just a thought.

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