  Radar and spacecraft observations show the permanently shadowed regions
around Mercury's North Pole to contain water ice and complex organic material.
One possible source of this material are impacts by interplanetary dust
particles (IDPs), asteroids, and comets.
  We have performed numerical simulations of the dynamical evolution of
asteroids and comets over the few Myr and checked for their impacts with
Mercury. We use the N-body integrator RMVS/Swifter to propagate the Sun and the
eight planets from their current positions. We add comets and asteroids to the
simulations as massless test particles, based on their current orbital
distributions. Asteroid impactors are assigned a probability of being
water-rich (C-class) based on the measured distribution of taxonomic types. For
comets, we assume a constant water fraction. For IDPs, we use a dynamical
meteoroid model to compute the dust flux on Mercury. Relative to previous work
on asteroid and comet impacts (Moses et al. 1999), we leverage 20 years of
progress in minor body surveys.
  Immediate post-impact ejection of impactor material into outer space is taken
into account as is the migration efficiency of water across Mercury's surface
to the polar cold traps.
  We find that asteroids deliver $\sim 1 \times 10^{3}$ kg/yr of water to
Mercury, comets deliver $\sim 1 \times 10^{3}$ kg/yr and IDPs deliver $\sim 16
\times 10^{3}$ kg/yr within a factor of several. Over a timescale of $\sim 1$
Gyr, this is enough to deliver the minimum amount of water required by the
radar and MESSENGER observations.
  While other sources of water on Mercury are not ruled out by our analysis, we
show that they are not required to explain the currently available
observational lower limits.
