Another follow-Up to this [question](https://worldbuilding.stackexchange.com/questions/22844/sol-economy-what-is-optimal-for-production-on-earth).

If you exclude earth as source, which means you can use all other planets and all celestial bodies within neptunes orbit range.

**Just how hard it is to get your hands on clean / useable or drinkable water? Can it be harvested? Or somehow manufactured out of other elements that are more readily available? Dynas had the idea to use water as a currency. Is it valuable enough?** 

I believe comets could be a source (since they are made of ice?). 
If you have a better idea for a currency, please answer the other question [here](https://worldbuilding.stackexchange.com/questions/22844/sol-economy-what-is-optimal-for-production-on-earth). Thanks!