[Ben Krasnow's] friends always want him to bring a fire extinguisher to their parties, not for safety reasons, but to quench their thirst. You see, [Ben] uses old fire extinguishers as kegs for his home-brewed beer. They’re not all that different from the Cornelius kegs that most home brew setups use; they’re intended to dispense liquids under pressure, include a liquid exhaust valve, and a gas pressure valve. All he had to do was clean the stainless steel parts extremely well, replace the gaskets, and modify the input valve to use a quick connect for his CO2 system. For good measure he also added a low pressure meter to let you know the carbonation level.
Recently, he installed a home tap system that uses two of the extinguisher kegs. Our favorite part is the refrigerated hose loop that uses a fan to circulate cold air from the fridge all the way to taps.