holding multi tonnage of water
No small step there getting that water into orbit.
this is a solar system ship...a huge non take off and landing type of vessel meant for moving large amounts of people/freight...you take off and land with separate small units...get just enough water on board to mine the ice farther out in the solar system..either from Keiper belt ice or in closer from ice moons(europa etc) that have much lower gravity to fight...