  The Earth contains between one and ten oceans of water, including water
within the mantle, where one ocean is the mass of water on the Earth's surface
today. With $n$-body simulations we consider how much water could have been
delivered from the asteroid belt to the Earth after its formation. Asteroids
are delivered from unstable regions near resonances with the giant planets. We
compare the relative impact efficiencies from the $\nu_6$ resonance, the 2:1
mean motion resonance with Jupiter and the outer asteroid belt. The $\nu_6$
resonance provides the largest supply of asteroids to the Earth, with about
$2\%$ of asteroids from that region colliding with the Earth. Asteroids located
in mean motion resonances with Jupiter and in the outer asteroid belt have
negligible Earth-collision probabilities. The maximum number of Earth
collisions occurs if the asteroids in the primordial asteroid belt are first
moved into the $\nu_6$ resonance location (through asteroid-asteroid
interactions or otherwise) before their eccentricity is excited sufficiently
for Earth collision. A maximum of about eight oceans of water may be delivered
to the Earth. Thus, if the Earth contains ten or more oceans of water, the
Earth likely formed with a significant fraction of this water.
