  Between May 2016 and September 2018, the intermediate polar (IP) FO Aquarii
exhibited two distinct low states and one failed low state. We present optical
spectroscopy of FO Aquarii throughout this period, making this the first
detailed study of an accretion disc during a low state in any IP. Analysis of
these data confirm that the low states are the result of a drop in the mass
transfer rate between the secondary star and the magnetic white dwarf primary,
and are characterised by a decrease in the system's brightness coupled with a
change of the system's accretion structures from an accretion disc-fed geometry
to a combination of disc-fed and ballistic stream-fed accretion, and that
effects from accretion onto both magnetic poles become detectable. The failed
low state only displays a decrease in brightness, with the accretion geometry
remaining primarily disc-fed. We also find that the WD appears to be
exclusively accretion disc-fed during the high state. There is evidence for an
outflow close to the impact region between the ballistic stream and the disc
which is detectable in all of the states. Finally, there is marginal evidence
for narrow high velocity features in the H$\alpha$ emission line during the low
states which may arise due to an outflow from the WD. These features may be
evidence of a collimated jet, a long predicted yet elusive feature of
cataclysmic variables.
