A standpipe is a large vertical pipe into which water is pumped as to produce a desired, uniform pressure in a water-supply system. In the world of firefighting, a standpipe is the rigid water piping that is built into multi-story buildings to which fire hoses can be connected. To put in terms that might be easier to understand, within the context of a building, a standpipe serves the same purpose as a fire hydrant that you would see on the street.