You "guess" right.
Putting the issue of "colonization" aside for a moment...
If scientists ever want to establish a long-term base on either the Moon or Mars, it would be VERY, VERY convenient to be able to tap local sources of water. Besides needing drinking water, there's also a need for water for purposes of, e.g., irrigation. Because how could you possibly establish a self-sustaining, long-term research station on either the Moon or Mars without growing your own food?
Water can also be subjected to electrolysis to produce breathable O2.
Water could also be used either as an inert propellant (heated by nuclear energy to produce steam), or as a feedstock for various other industrial purposes.
The possibilities are endless...
Regards,
As far as water available in space is concerned, I hold that if we fail to leave cradle Earth and TRY to live elsewhere, we are failing to grow. Closed systems, the ones without frontiers, are ones with authoritarian governments and I regard that as a bad thing.
So it is good to find water on planets and moons but match capabilities to horizons. In open space there are comets and the remains of comets. Most comets have masses in millions of kilograms and water forms a large portion of their content. While their capture / redirection is beyond our current technology, a mere 117 years ago there was no sustained heavier-than-air flight! Could we crash a redirected comet into the moon in the next century? Would you bet against it?