No cheers for my idea of mining the Sun for hydrogen? Oh well! So okay, here's another way to make water:

NH₄NO₃ (aq) + KOH (aq) → NH₃ (g) + KNO₃ (aq) + H₂O (l)

Of course, you then have to heat the resulting solution (the NH₃ will float off as a gas) and turn the water in it to steam, but that could be distilled for drinking water.

No, no, don't thank me! Knowing that I introduced more KNO₃ into the world is enough.