Manmade water is not very difficult to produce (I guess it would depend on your definition of manmade, it isnt really man making it, the chemicals arrange themselves into water).
Burning Hydrogen gas with Oxygen gas will make pure water,
2H2 (g) = O2 (g) --> 2H2O (g)
This reaction is quite spontaneous (and explosive) one it has been ignited.
This is the reverse process of splitting water apart [through elelctrolysis] into H2 and O2.
Many other chemical reactions produce water as a product.
Similar to burning Hydrogen gas, burning Hydrocarons (example, Methane or Octane) also produced water [amongst other things].
Another exakmple would be a reaction between baking soda and vinegar. The reaction produces Carbonic acid (H2CO3) which quickly decomposes into Carbon Dioxide (bubbles) and water.
Acid-Base neutralizations produce water too.
The net ionic equation for the neutralization of a stron acid and a strong base is,
H+ (aq) + OH- (aq) --> H2O (l)