Historically, water guns were made of metal and used rubber squeeze bulbs to load and propel water through the nozzle
Many small water guns work on the same principle as a spray bottle. The body of the toy is essentially a container for water, and the trigger is attached to a pump which squirts water out of a tiny hole at the muzzle or nozzle. However, many modern water guns employ more complex technologies to provide more power and water output than their predecessors.
In the U.S. and Canada, for several years, import regulations and domestic laws have required squirt guns to be made of clear or tinted transparent plastic. This is to make them harder to mistake for actual firearms.
Modern variations of the design include using compressed air, rubber chambers, springs, peristaltic pumps, or hydraulic pressure to propel the water or an electric pump powered by batteries. Some employ a combination of technologies to produce better stream performance. A more common term for larger water guns is water blasters.
Perhaps the most recognized brand of water gun is the Super Soaker brand by Larami Ltd, now taken over by Hasbro Inc. There are also other notable water gun brands such as Water Warriors by Buzz Bee Toys Inc., Total X-Stream by Lanard Inc., and Shield Blasters by Mattel Inc.
Squeeze Bulbs: Akin to water droppers, the oldest known manufactured water guns utilized a simple rubber squeeze bulb into which water could be drawn, then forcibly expelled out the nozzle by squeezing the bulb rapidly. This design has inherent limitations regarding the amount of pressure that one can achieve (fully dependent on the user's hand gripping strength) as well as the need to refill after each shot.
Trigger Pump / Spray Bottle: Many of the earlier small water guns used the same trigger based pumping mechanism as seen on spray bottles. Basically, the trigger would actuate a positive displacement pump shaft. With the aid of two check valves, often using small ball bearings, fluid could be drawn into the pump from a reservoir, then forced out the nozzle upon squeezing the trigger. The simplicity of the spraying mechanism meant these types of water guns could be manufactured rather cost-effectively and that the majority of the body could be used as the reservoir. The primary limitation with this design is the volume of water that could be effectively moved per pump. Increasing pump volume would require more user effort to push the fluid out, making larger designs impractical. However, this technology remains widely used today both in spray bottles as well as small water guns that can be found in a wide variety of shapes and colours.
Syringe / Piston: Another simple method employed in a number of water guns to push water is a syringe or piston type system. In essence, the water gun is made up primarily (sometimes exclusively) of the pumping mechanism that comprises an outer pump shaft with an inner pump-rod and water-tight seal. This allows water to be drawn into the pump as the pump is extended, then forcibly ejected out as the pump is compressed. Stream performance is dependent on the user's strength. Some models, like the Super Soaker Power Soaker Jr. and Stream Machines draw in and expel water out of their nozzles. This design means that a bucket-type filling source is needed in order to fill and refill the water gun. Other models, like the Super Soaker Power Soaker Mighty Cannon and Water Warriors Steady Stream, come with a couple of check valves and a reservoir for true portability.
Motorized: small piston: During the 1980s, the motorized water gun was perhaps at its most prolific time. Companies such as Entertech Inc. and Larami Inc. were creating replica-type water guns modeled after guns popularized in movies such as Rambo. At the heart of these blasters was a small motor and crank shaft that would convert the rotary motion into a forward-backwards pumping motion to drive a small pump akin to those found in the small spray bottle-type squirt pistols. While stream performance was often not particularly better, the fact that the motor took away the user's need to pump made for their increased popularity despite the fact that these water guns typically burned through 4 AA batteries over the course of a couple of water fights. However, their main strength and consequent reason for dismissal was their realistic styling. After some of these realistic-shaped water guns were attributed to accidental shootings by police, stricter rules regarding shapes and colouring of water guns were drafted in the United States.
Air: Pressurized Reservoir: This system was made famous by the Super Soaker brand of water guns, but actually was first employed by the Cosmic Liquidator. In this case, a pump is used to push air into a partially water-filled reservoir. The reservoir is otherwise air-tight, but has one valve to let the incoming air in from the pump as well as a manually controlled valve operated by the user, commonly activated by pulling on a trigger. As more air is pumped in, the air in the reservoir is compressed, increasing in pressure; the water is also pressurized by the now compressed air. Upon opening of the nozzle valve, the pressurized water is then pushed out through the nozzle as the air attempts to re-equilibrate with atmospheric pressure. This system allows pumping energy to be stored and used as needed. As well, unlike the methods noted above, this air pressure system allows production of a solid, continuous stream of water.
The limitation of this design is that a large number of pumps can be required to pressurize a larger reservoir. As well, poorly sealed reservoirs would render a water gun useless. Moreover, these water guns cannot be refilled unless emptied and depressurized. Opening a pressurized reservoir blaster while there is pressure remaining in the system can result in lots of local water spray or even an unexpected launch of the water gun and/or reservoir out of one's hands.
Air: Separate Pressure / Firing Chamber: The air-based separate pressure chamber or firing chamber system works on the same physical priniple as the pressurized reservoir system, but instead of pressurizing the reservoir, a separate, fixed volume chamber is included on the water gun into which water is pumped, compressing the air inside. This technology was first used on the Super Soaker SS 100. What this allows is for the reservoir to be removed/opened at any time for refilling since the reservoir is not pressurized. As well, the typically smaller size of the pressure chamber and the fact that water is typically pumped as opposed to air reduces the average number of pumps needed to achieve functional pressure. For improved performance, some users opt to pre-pressurize the firing chamber by pumping in some air first. This increases the starting pressure within the chamber, thus increases the overall average pressure experienced by the water when it is pumped into the pressure chamber.
Air: Split Air vs Water Pressure Chamber: While air based, the split air vs water pressure chamber has a sliding plunger that separates the compressed air from the water. This technology has so far only been seen on the Water Warriors Aqua Master PreCharger Series. A button is used to toggle whether the pump is priming/pre-pressurizing the pressure chamber with air or whether the pump is moving water into the pressure chamber. Akin to pre-pressurizing the Separate Pressure Chamber water guns, the split air vs water pressure chamber takes this one step further by preventing the accidental, undesired release of the pre-pressurized air by keeping it separated from the water by a sliding piston divider. After all the water is expelled from the pressure chamber, the sliding piston prevents loss of the pressurized air, thus reducing the number of times the water gun must be pumped with water in order to achieve optimal firing pressure.
Constant Pressure System: The Constant Pressure System (CPS) was first introduced by the Super Soaker CPS 2000 in 1996. Instead of relying on pressurized air to push water out the nozzle, CPS uses rubber elastic chambers to power the water gun. There are two common shapes of CPS chambers used: cylindrical and spherical. While the physics behind the system remains the same, there is a slight advantage for the cylindrical shape to push water in a linear direction since, upon expansion, it has more elastic force vectors pointing in the desired direction of flow compared to a spherical pressure chamber. However, because of how they expand, cylindrical pressure chambers also have more stress points than spherical ones. Nevertheless, use of the elastic materials typically offers improved power performance, particularly since pressure does not drop off as quickly as water is expelled from the pressure chamber as is seen in air-pressure-based systems. CPS-based water guns are perhaps some of the most sought after due to their improved performance and lack of firing angle limitations.
Rubber Diaphragm / Hydro Power: "Hydro Power" is a term coined by Buzz Bee Toys Inc., referring initially to their series of water guns that employed a elastic rubber bladder to pressurize water. Akin to the CPS system, the rubber diaphragm system can be considered basically half of a CPS-pressure chamber. A sheet of elastic material (typically rubber) is clamped against a housing unit. Water is pumped into the chamber, expanding the bladder that pressurizes the water within. However, due to the shape of the bladder, its expansion is not as uniform as in the CPS system, thus it experiences more significant pressure dropoff as the pressure chamber empties.
Springs: Another means of pressuzing or propelling water used in some water guns is the use of metal springs. The Waterball series has a spring-based catapult mechanisms for launching balls of water out of its nozzle. The Water Warriors Steady Stream uses a spring-based mechanisms as a sort of water capacitor to allow this otherwise piston-based water gun to produce a constant stream of water so long as the user pumps quickly enough. Additionally, the Super Soaker Quick Blast employs a spring-based firing chamber to propel its stream forward.
Peristaltic Pumps: Peristaltic pump systems have also been used in some water guns models, most notably the original Shield Blaster water guns by Mattel Inc. In this system, a rotary pump is used to move rollers along a compressible piece of tubing. As the rollers move along the tubing, they push water along. The force exerted by the pump is dependent both on the speed of rotation as well as the thickness of tubing used. True continuous streams cannot be produced since the physical presence of the rollers means there will be partial gaps in the flow. However, if pumping is done quickly enough, the end result is a virtually smooth stream. .
Hybrid Systems: There are also a number of water guns that employ a variety of pressurization systems to propel water.