At our place, we have simulated a similar system.
The steps we followed were:
Create a block of solid (say Iron) and cut out the shape you want and write out the coordinates.
Create an fcc latice of points, such that number density of points = number density of water molecules you desire.
Cut out a hollow in this lattice, such that the solid will be able to fit in this hollow, along with some tolerence.
Write out these coordinates.
Replace each point written out with a water molecule, using a simple script/ C code.
Merge the solid and water files into an input data file.