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Is it possible to weaponize common tap water in some sort of gun?

Imagine a basic water gun. It doesn't do much damage at all.

But what if we could fire the water out in controlled spurts, at high speeds? Imagine a highly complex water gun. This gun internally controls the amount of water in each shot, and propels said amount of water in a given direction, allowing the water to be used as a projectile.

What are the limitations of this weapon, how much damage could it potentially do, and how would it work?

Note: This weapon must not fire ice. It must fire the LIQUID form of water.

  • Range wise, I'm looking at preferably bow and arrow range or higher - definitely not close range.

  • What if we used the water as the "weight" behind the projectile, and a small plate/cone/something were used as a "barrier" in order to stop the water from getting deformed due to air resistance? Would this weapon be plausible?

  • As long as it's liquid water hitting the target, it passes the "this weapon fires liquid" test.

  • When designing this weapon, even if we currently don't have the technology to actually make it, as long as the technology is sound and the physics/theory works out, it's okay. (It's okay to go slightly into future tech, but don't think up something you can't explain)

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  • $\begingroup$ A bit of an unusual case, but in very cold climates, simply soaking an opponent could be dangerous because of increased heat transfer. It would need to be combined with control over indoor locations, though. $\endgroup$ – user3757614 May 20 '15 at 0:03
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    $\begingroup$ Riot cannons are probably where you'll end up, but they're not lethal. The main purpose is to disperse groups of people without hurting them. $\endgroup$ – Erik May 20 '15 at 5:02
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    $\begingroup$ @Erik Without seriously hurting them. But my understanding is that being hit by a water cannon is painful and, of course, it can cause falls which may lead to more serious injuries. $\endgroup$ – David Richerby May 20 '15 at 10:16
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    $\begingroup$ Water cannons aren't lethal because they shoot X ammount of water in a Y area, resulting in less pressure than if you'd shoot the same ammount of water in a Z area where Z<Y. Decrease the area, and you've just increased the pressure, and thus, perfutation power and as such, lethality $\endgroup$ – Oak May 20 '15 at 12:12
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    $\begingroup$ I am definitely surprised that the government of some country at some point in time has not worked on weaponising water. $\endgroup$ – the_OTHER_DJMethaneMan May 20 '15 at 14:44

19 Answers 19

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You've experienced water flying through the air at its eventual maximum speed.

Rain. This is water at its terminal velocity.

Gravity is trying to constantly accelerate the falling water, but that force is matched by the wind resistance and the water will not go any faster.

Starting slow, it will reach that speed. Starting fast, it will reach the same speed. It's the point at which the forces equal out.

You can pressurize the water, like with a water cutter:

enter image description here

But the water will rapidly break into droplets and slow down, within several meters, to (at best) its terminal velocity. Without a constant force behind it to counteract wind resistance, the best you'll get is rain.

The only way to weaponize water droplets is to add poison to them or make them very hot. Either one will be fairly lame, poison is cheating and the hot water will rapidly cool.

You could do drop all the water from a rain cloud at once. It's technically in a discrete packet and utterly destructive.

enter image description here


Edit: Using the water as the weight is also not great. It's not really the water doing the damage and there are far denser materials that could be used which would work far better due to inherent structural stability and the higher mass per unit volume. The penetration of something with the density of water would be poor due to impact depth approximations.

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    $\begingroup$ Make it really cold, and deliver it in large chunks.... $\endgroup$ – Oldcat May 19 '15 at 23:02
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    $\begingroup$ @Oldcat Sure, freezing helps, but is against the rules for the question. $\endgroup$ – Samuel May 19 '15 at 23:04
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    $\begingroup$ Terminal velocity only applies if the only forces acting on the water are air resistance and gravity. $\endgroup$ – superluminary May 20 '15 at 10:49
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    $\begingroup$ superluminary is correct. Yes, the water will eventually be going downwards at its terminal velocity, if we assume it has time and space to do so. But we can't really assume that for the same reason we don't assume bullets move at their terminal velocity when hitting the target. Effective range of weapons is usually far shorter than what is needed to reach terminal velocity. Talking about terminal velocity as absolute limit is also misleading since it varies with the droplet size. Drag increases with square and weight with cube of size so larger droplets have higher terminal velocity. $\endgroup$ – Ville Niemi May 20 '15 at 15:10
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    $\begingroup$ @superluminary So what if there were a way to make it so that the water passes through an area with little air resistance? Perhaps this gun would be a good weapon in space? $\endgroup$ – Aify May 20 '15 at 15:34
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There is something which contemporary police forces already use for riot control: a water cannon.

French officers using a water cannon 4 years ago. image by The Sun.

French officers using a water cannon 4 years ago. Image by The Sun.

This does not see that much use in the US, but in the EU and Asia, this nonlethal weapon is often used to help control riots. A riot-grade water cannon can shoot 20 liters of water per second for nearly 10 minutes. Earlier iterations of water cannons have been known to knock protesters over and tear their clothes. some protesters have even been permanently blinded by the sheer force of the water. A water cannon is basically a large-scale jet cutter.

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Water alone is not enough: you need either ice or steam. There are several steam options below which would probably work well together:

  • As other answers have pointed out, squirting out water at high pressure makes a water jet cutter. An 'abrasive' water jet can cut stone and metals! You might also have seen high pressure cleaners that take a bucket of water and squirt it out 10 meters. They however are not really all that dangerous.

  • Supercritical water oxidation
    Pressurise your water to 22-23 MPa and heat it to 380°C and you have, as Winchell Chung put it: "hellfire-in-a-box". Since you wont be able to get your enemies into the box, you will have to use a very high pressure squirt gun to weaponise a SCWO. This may or may not be feasable depending on your setting.

  • High pressure steam, which has been vapourising people since the 1800's! As you may already know, the boiling point of water changes with atmospheric pressure. At the top of Mt. Everest (34kPa) for example water boils at 71°C. At high pressures, like in a steam engine or SCWO, water boils at a higher temperature. This straightdope article has relevant information on the dangers of high pressure steam. If you have a pressure chamber with boiling water and it ruptures, then BOOM, you have a steam bomb. Squirting water out of a SCWO (above) would produce a large gout of high pressure/temperature steam.

So you can weaponize high pressure and temerature water by shooting it out of a pressure vessal, technically this gun shoots water, which immediately becomes steam, which then cools to become merely boiling water. Firing in spurts would allow the weapon to build up pressure between 'squirts'.

I would like to note that this steam/water weapon will be a short range weapon, limited to a few tens of meters at most. The weapon would produce buring death in a large area and could potentially kill the person firing it as well... Do not use this weapon in small rooms :P.

A weapon that kills or maims with only liquid water is not feasable. There are several other ways of weaponizing water or anything else: Velocity, Mass, Temperature.

  • Velocity is all well and good, but your water jet will quickly become mist rather than a usable weapon. This negates Piercing Damage because the water's impact against the target is spread out. The water will also spread too quickly to produce serious blunt damage. One commenter (HadesHerald) on your question suggested frezing the outside of your jet of water to help it retain its shape. This is somewhat feasable but you don't want ice.

  • Mass: also known as dropping a swimming pool on top of the target. This is quite destructive, especially when combined with Velocity and Temperature, but could be impractical for your weapon.

  • Temperature: Melting or vapourising your target is your best bet. High pressure/temperature steam can cut through meaty flesh, cook you from the inside or burn your lungs so you suffocate. Fun!.

As you can see, I recomend high pressure and high temperature steam. Your weapon might be a lot like a flame-thrower that produces steam or a gun that squirts water at very high pressure.

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I think I have to go with No, not feasible.

Water does not hold an aerodynamic form in flight...the air resistance will reshape it and see much of the liquid water convert to gas mid-flight. If you could get this up to supersonic speeds (not easy given waters properties...non-magnetic being a biggie) it'll likely evaporate long before it could hit a target.

The only real weaponization use of water that I can see gets into the water cannon, which is more due to the mass of water pushing around the target as opposed to actually damaging the target.

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  • $\begingroup$ Can you show some evidence for water not holding an aerodynamic form in flight? Droplets of water came to mind when I read your answer - they seem to be able to fall through the air just fine - why can't we just make them fall... sideways? $\endgroup$ – Aify May 19 '15 at 22:41
  • $\begingroup$ @Aify I present no evidence, but my answer includes an explanation of the basic reason. $\endgroup$ – Ville Niemi May 19 '15 at 22:50
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    $\begingroup$ Droplets aren't very aerodynamic and can reach a max speed of around 9 m/s when falling before air resistance negates gravity. Much of rain fall actually doesn't strike the surface either, it evaporates before it hits the ground. I'll see what I can find in evidence, but a drop of rain accelerated and thrown through the atmosphere will become gas readily. $\endgroup$ – Twelfth May 19 '15 at 22:52
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    $\begingroup$ @Aify: The size of the droplets actually correlate with the speed the water travels at. When you accelerate a droplet above a certain speed it breaks up into two. If you accelerate rain to the speed of sound it will break up into water vapor. $\endgroup$ – slebetman May 20 '15 at 8:47
  • $\begingroup$ Yea... the limitation on that is an interesting one to try and bypass isn't it ;) Although, @slebetman now i'm thinking of a new question for a vapor weapon... $\endgroup$ – Aify May 20 '15 at 14:13
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What sort of range do you require?

You could use bomb-disposal equipment that blasts water at the triggering mechanisms. It propels water so fast it destroys the circuitry faster than it can fire.

Limitations:

You'll need water. You'll also need explosives. These weigh down the operator, and you can run out of them. Short range. Friction, surface tension and viscosity of water will make it form droplets. These droplets will slow down. Basically, they'll turn into raindrops.

Advantages:

Short range is actually a nifty safety feature. Bystanders downrange of the projectile are pretty safe. Be sure to bring an umbrella.

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  • $\begingroup$ See Edit for range clarification. $\endgroup$ – Aify May 19 '15 at 22:48
  • $\begingroup$ Explosives? I thought those things were basically modified shotguns--driven by gunpowder, not high explosives. $\endgroup$ – Loren Pechtel May 20 '15 at 4:32
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    $\begingroup$ @Loren, gunpowder is an explosive. $\endgroup$ – user6511 May 20 '15 at 4:47
  • $\begingroup$ @user6511 Gunpowder is more an extremely rapid burn than a true explosion. Try putting C4 in your gun and see what happens! $\endgroup$ – Loren Pechtel May 20 '15 at 15:36
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I'll expand a bit on the answers by Twelth and Shalvenay. The basic issue is that since water is fluid and the speed of sound in air is much lower than the speed of sound in water and any supersonic projectile creates a conical shockwave, the water bullet will spread into a conical shape matching the shape of the shockwave. This will rapidly increase air resistance.

Note that this is not due to air vaporising the water, this is due to the pressure ahead of the projectile being much higher than on the sides and pushing the fluid to the lower pressure. So no a solid shock plate or cone would not help, you'd need to cover the sides to contain the water and prevent it from spreading.

There are two exceptions to this. First the water jet cutters mentioned by Shalvenay create a continuous stream of water. In a jet the medium water is pushing is also water that has the exact same speed of sound. So as long as you start below speed of sound in air and wait until the stream hits the target, you can increase the speed all the way to the speed of sound in water. Or simply waste water by pumping it faster while the jet reaches the target at speed of sound in air. Which is high enough that the jet is quite useful.

Second is simply that the expansion takes time which means distance. So if your target is close enough you can get an useful effect. A short range water hammer essentially. This could be useful for breaking doors or locks for example. Or as user6511 says bomb disposal. Although a shaped charge does the same and is mature technology.

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    $\begingroup$ Alright, clearly this question is going to end with a flat out no as an answer, so I'm going to add an edit real quick to (hopefully) make it possible. $\endgroup$ – Aify May 19 '15 at 22:52
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    $\begingroup$ @Aify If you are drastically changing the question it is better to make a new one. Major edits to question make old answers incomprehensible. $\endgroup$ – Ville Niemi May 19 '15 at 22:55
  • $\begingroup$ It's an extra add on - not a new question. I don't believe i've invalidated any of the previous answers by adding it. However, if I am wrong, please tell me and I'll start a new question with it instead. $\endgroup$ – Aify May 19 '15 at 22:59
  • $\begingroup$ Ah, but if it did cover the sides - it would work? Assuming there were a way to accelerate quickly enough, that is. $\endgroup$ – Aify May 19 '15 at 23:01
  • $\begingroup$ @Aify That is just a normal bullet with liquid filler. I think there are liquid point bullets, actually. Although the liquid is not water IIRC. $\endgroup$ – Ville Niemi May 19 '15 at 23:03
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In the comments, @HadesHerald made the best suggestion I've seen here. The projectile COULD be made of ice that is carefully calculated to melt immediately before impact.

If necessary, it could be composed of multiple layers, all frozen to different temperatures. Potentially, the core could even be liquid initially.

Then the only limit on speed/distance the projectile can travel is absolute zero.

Even if we can't rely on the water to pierce a body, the momentum alone would be enough to cause fatal damage if the speed x mass were high enough.

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  • $\begingroup$ Since when is absolute zero a limit of speed and/or distance? Otherwise, nice answer! $\endgroup$ – ArtOfCode May 20 '15 at 13:11
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    $\begingroup$ @ArtOfCode Sorry, that was a sort-of shorthand. What I mean is, If you freeze the entire projectile solid at absolute zero and you can fire it, say 100 miles before it all melts, then you can't freeze it a bit lower to get it to go farther, but any distance up to 100 miles can be perfectly achieved with a particular temperature - or layers of temperatures. $\endgroup$ – Lefty May 20 '15 at 13:50
  • $\begingroup$ You could always make the initial projectile bigger, with outer sheets melting/subliming during flight and only a core actually reaching the target. $\endgroup$ – M.Herzkamp May 21 '15 at 13:50
  • $\begingroup$ @M.Herzkamp, really good point - making it bigger at the start would allow it to fly further. I was automatically envisaging trying to keep the same bore size but there's no need for us to worry about that since it's only a thought experiment! $\endgroup$ – Lefty May 21 '15 at 18:52
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Water rapidly loses velocity and pressure in atmosphere. However, if the rules allow the water to be wrapped in a shell, you could create an extremely lethal device: a pressurized bullet.

First, place the water in a spherical chamber. Using pistons, pressurize the water to the point the chamber can barely withstand the pressure. Plug the chamber (a metal plug already inside the chamber would work best).

Then, fire the bullet. When the water-filled chamber impacts, the intense pressure will cause the sphere to rupture, spraying shrapnel and water. More importantly, if the bullet hit a fleshy target, it will do serious damage add the pressurized water decompresses.

Alternately, the container could be a syringe; on impact, it drives a quantity of pressurized water into it's target. Essentially, this gun fires a water cutter.

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  • $\begingroup$ water is extremely hard to compress. 1mile down in the ocean it will be 1% compressed. Hardly weapons-grade. water Compressibility $\endgroup$ – NERVA May 21 '15 at 18:25
  • $\begingroup$ While water is, indeed, very hard to compress, it is possible. It would take a lot of energy, and some incredibly strong machinery, but it is possible. Useful, though? Probably not. $\endgroup$ – ArmanX May 21 '15 at 18:45
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Basically, what you are describing would be a weaponized form of a water jet cutter. The main limitations that would make such a thing impractical are the weight of all that water (industrial cutters are plumbed instead as they need a high volume of water to work) and the rapid effectiveness falloff due to the jet losing pressure.

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Shaped vortex in air

As many posters have correctly pointed out, the issue with a high speed water projectile is that as a fluid it will rapidly fragment and become less aerodynamic. If it breaches the speed of sound it will be vapourised by the shockwave.

Create a focussing vapour conduit

One solution to this would be to create a conduit in the air prior to firing the projectile. A stream of vapour rings could perhaps be used as lenses to refocus the water pulse as it travels.

I don't know if this would work or not, you'd have to try it, but it might.

Weapon characteristics

This would be a short range weapon, it would perhaps only fire a few meters across a room. It would also require fairly still air. A strong wind would bend the vortex. There would be a short warm up time before the shot while the vortex was established.

This would be a very high tech weapon. A society would need to be fairly advanced to perfect it.

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Water cannons are widely used as a crowd control weapon. Both purpose-built police equipment and repurposed firefighting equipment can be used in this way. Water cannons can cause severe injuries, but they are not a particularly effective tool for doing this; their main purpose is to inflict pain, inhibit movement and coordination, break formations, and provoke fear.

The HowStuffWorks article on water cannons contains some information on their typical range and power, as well as their basic engineering. The Guardian article linked above also mentions a few technical details.

Many people in the U.S., I think, strongly associate water cannons with the police response to the Birmingham campaign of 1963. They're ubiquitous in images and descriptions of the campaign.

Although they're deployed for crowd control mainly on land, water cannons have also been fired against unarmored boats, like fishing vessels. Some reports suggest that small boats can be damaged or flooded with water cannons.

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As plenty of people have pointed out, it's totally unfeasible to fire liquid water a long distance and have it hit hard.

However, I think that there is a pretty good option if we allow multi-stage weapons. A water balloon could be fired fairly far. Put a small explosive in it, and detonate it when it gets near the target. This multiplies the force of the pressure wave from the explosive, because water is, compared to air, effectively incompressible.

Maybe that's cheating. That said, it's the only reasonable way for liquid water to deliver a strong impact at long range. More energy could be delivered with a rigid (glass?) Container and a shaped charge.

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Forest-fire fighting helicopter with water drop bucket. Multiple shot, controllable effectiveness from non-lethal crowd control to absolutely deadly kinetic street sweeper.

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    $\begingroup$ While this does qualify as an answer, it could do with some more expansion: why is this method better than others? How might you control the 'shot' power? $\endgroup$ – ArtOfCode May 20 '15 at 15:08
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Since the fundamental limitation is based in physics, we will have to cheat a bit. One comment upthread mentioned a water balloon, and that is essentially what you will need to make this more useful as a weapon than a water jet cutter (which essentially works at point blank range).

The water needs to be encased in something which will contain it and protect it from direct interaction with the air or any shockwaves produced as it passes the sound barrier. Depending on how far and fast you actually want to go with this, the projectiles can range from sponges and water balloons (generally slow and short ranged, but if the projectile is large enough to hold a lot of water, the sheer momentum of impact could do a lot of damage). On the far end of the scale, an artillery shell designed to fire flares or leaflets could be used as a carrier shell for your water. If the base eject plug is released and water simply pours out, it will rapidly disperse as in all the other examples, so even here the water needs to be contained in some sort of sub munition. Mind you, a submunition the size of a pop can moving at near supersonic velocity will pack a lot of kinetic energy as it strikes, which will rip the thin skinned metal container open to release the water after all....

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Why not think about changing the nature of the water molecules themselves? I would look at exploring various options of creating hydronium?

From Wikipedia:

Hydronium is the cation that forms from water in the presence of hydrogen ions. An acidic solute is generally the source of these hydrons; however, hydroniums exist even in pure water. This special case of water reacting with water to produce hydronium (and hydroxide) ions is commonly known as the self-ionization of water. The resulting hydronium ions are few and short-lived.

Hydronium is very acidic: at 25 °C, its pKa is -1.7. It is also the most acidic species that can exist in water (assuming sufficient water for dissolution): any stronger acid will ionize and protonate a water molecule to form hydronium. Unlike hydronium in neutral solutions that result from water's autodissociation, hydronium ions in acidic solutions are long-lasting and concentrated, in proportion to the strength of the dissolved acid.

The rest of the gap could be filled by a more competent physicist/chemist/engineer...

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So far, many of the answers seem to be in unison: no, not feasible because the water stream falls to bits and becomes useless rain.

Water Cannon

I see this not as a flaw, but as a design specification for a weapon. I don't see weaponised water as discrete "bullets", but rather as particle stream. Consider the World's Largest Water Cannon. This one shoots about 70k litres of water per minute as a fire fighting tool. That's a bucket load of water! And it's useful range is about 200m.

In order to weaponise, one strategy would be to multiply the basic system by perhaps eight. This weapon system, delivering as much as 560k litres per minute in a concentrated area would certainly be able to clear the deck of an attacking vessel and may even be able to deliver enough water to swamp & sink a small vessel. The curtain of water acts as a shield, foiling the enemy's attempts to fire and manoeuvre. The pressure of so much water might even cause physical damage to, for example, the bridge of the enemy vessel, rendering it useless. Used in conjunction with other conventional weapons and I think you'd have a viable system that combines offensive capability & defensive screening.

Basically this idea is simply the anti-piracy water cannon principle on steroids.

Another possibility for weaponising water:

The Dam

Throughout human history, people have lived along rivers. Say two rival city states inhabit a stretch of river. Their wars have been ongoing for decades and neither side seems to be able to gain the upper hand. Now let's say some clever genius comes along and tells an ancient myth from a far distant land about how the whole country was flooded by the gods and wiped everyone away.

The archon will say, nice story, but how does that help me?

The wise genius says: take the beaver as your totem and build a huge dam across the river, with just enough outlet to keep some flow going downstream.

Once you've got a nice reservoir built up, break the supports and the let the dam fail. Gouts of water and debris rush down stream, wiping out your rival city-state!

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WATER AS A BOMB


Well, water is made up of 2 atoms of Hydrogen & 1 atom of Oxygen if we separate them (process is called Electrolysis) and somehow able to use Oxygen to create fire, it would be better than water gun. Like a Bomb which consist of two parts, in First part there will be something which easily ignites(like rubbing two stones) spark and the Second part consist of Oxygen derived from Electrolysis of water. But the problem is that it should be done at a greater scale(large amount of Energy required for Electrolysis) and the Advantage is that Hydrogen is also an explosive gas.

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    $\begingroup$ This fails to meet the requirement of firing a liquid form of water. $\endgroup$ – HDE 226868 Sep 7 '15 at 18:14
  • $\begingroup$ If we assume an atmosphere similar to that of Earth, you don't need to add extra oxygen to make $\text{H}_2$ go boom. Look at Hindenburg. But, like HDE wrote, this fails to meet the criteria in the question; the OP wants something that, when it is fired and when it hits the target, is liquid water. $\endgroup$ – a CVn Sep 7 '15 at 20:47
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The biggest problem is the water losing energy too quickly as it deforms. I have a few ideas on this. You need to add some kind of bonding agent. We have real world thing you can add to water to keep it together, but I see the most potential in say electrically charged powder and a magnetic field sheath. On firing, the weapon would contain the water in a magnetic field that would let it hold it's shape longer, but not far. Liquid water is just not a suitable long range weapon. Even if it's doable, it's just not as good as other options at the tech levels.

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  • $\begingroup$ You're not going very far by containing water with magnetic fields. You would need a field of frog-levitating proportions, which would be a much more powerful weapon all by itself. Essentially, you would be adding cyanide to A-bombs. $\endgroup$ – LSerni Dec 24 '17 at 14:58
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How about a more si fi take with a sort of electro kennetic fused substance that can allow it to continuelessly push a stream at high velocity, maybe connect it to neuro tech and get into some water bending xP

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  • $\begingroup$ I think your answercould be improved if you defined the terms you used like "electro-kinetic fused substance" and gave more precise and scientific ideas with rigorous enough reasoning (the question has the science-based tag). Right now IMHO it isn't very helpful to other users or the OP. $\endgroup$ – user44285 Dec 24 '17 at 9:14
  • $\begingroup$ Welcome to WorldBuilding! Please edit your answer to elaborate on the points you made. If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus Dec 24 '17 at 15:09

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