Squirt Guns came into their own with the advent of EM acceleration systems. With the use of similar coil/rail gun technology, a solution can be used the same way a beam weapon can, except at a fraction of the cost or energy use. Heavy liquid metal solutions can cut through many materials as quick if not quicker than some high energy weapons. There are two methods of propulsion for squirts: EM and High Pressure.
EM propulsion works the same way as a Coil/Gauss/Railgun. Most commonly a coil system is used. A stream of heavy magnetically projected liquid can be thrown quite a long way. The recoil is smooth while it is streaming, similar to that of a fire hose. Since the aperture of the squirt is fairly small, ammunition can usually put out a whole minute of stream at usable pressure, but is quite heavy according to the ammunition type. Squirts are usually quite bulky as well, because of the tank-like nature of their magazine. Often, squirts are used as nano delivery systems or "direct" chemical attacks. A direct chemical attack is one that doesn't evaporate or vaporize much and has a limited destructive area. Less chance of hurting non-combatants, and therefore more desirable in close combat situations.
High Pressure squirt guns work like traditional high power spray systems. This is a much shorter range, but has a larger variety of ammunition it can use since it can handle magnetically sensitive payloads.
Squirts are very good crowd control weapons, and for dealing with large amounts of enemies thanks to its streaming and spraying effects.