Water gun

A water gun (or water pistol, water blaster, or squirt gun) is a type of toy gun designed to shoot water. Similar to water balloons, the primary purpose of the toy is to soak another person in a game such as water warfare.

Historically, water guns were made of metal and used rubber squeeze bulbs to load and propel water through a nozzle

Traditionally, water guns have worked on the same principle as a spray bottle. The body 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. Modern variations may employ compressed air, rubber chambers, springs, peristaltic pumps, or hydraulic pressure to propel the water. Some even use an electric pump powered by batteries. Some employ a combination of technologies to produce better stream performance. A common term for large high pressure water guns is "water blasters".

For several years in the U.S. and Canada, import regulations and domestic laws have required squirt guns to be made of clear or tinted transparent plastic to make them harder to mistake for actual firearms.

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.

Many early small water guns used the same trigger based pumping mechanism used for spray bottles. In this type of device, the trigger actuates a positive displacement pump shaft. With the aid of two check valves, often using small balls, fluid is drawn into the pump from a reservoir, then forced out the nozzle upon squeezing the trigger. The simplicity of the spraying mechanism allowed these toys to be manufactured cheaply, and allowed the majority of the body to be used as the reservoir. The primary limitation with this design is the volume of water that can 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 colors.

...
Wikipedia