Water is:

• a source of oxygen for breathing
• a source of hydrogen for rocket fuel
• a source of hydrogen for fuel cells for power generation
• for drinking (obviously)
• for sanitation
• for growing food
• fantastic radiation shielding (important when you don't have an atmosphere to absorb solar radiation) - embed water tanks in your habitat walls or just mount them on the outside - nice layer of cancer prevention

So yeah, there's too many uses for water in space and it's really difficult to lift into orbit from Earth. Even if some future moon base starts producing an excess of water, it'll be used to resupply other space habitats or vehicles.