What they do with water from this jet propulsion is use it in many different ways, including as a tool. Remember the definition of tool use is to transport something external to the animal, to modify it somehow and to use it to effect a change on the environment or itself. Archer fish use water this way. They spit it from their mouth into the air and knock small insects off overhanging tree branches. When the insect falls into the water, the fish eats it.
Octopuses also use water but in a variety of ways that change their environment.
One way octopuses use water as a tool is to change the niches that they find in the landscape to make them into suitable shelter, into homes. An octopus will find a 'likely' place, but it is usually clogged with sand and the shape may not be appropriate. It will gather sand and small rocks into the area under the arm web and carry them out to the entrance of the home. Once there, it will tilt up the web, let go with the suckers and jet it all away with a blast of water from the siphon. For a smaller amount of material it may not carry but just jet water at it, much as we would sweep with a broom.