In fact, the price is "purely determined" by supply/demand in the scenario you gave. The monopolist is using their monopoly position to create artificial scarcity, thus driving up prices. This is consistent with the law of supply and demand.
> would that indicate the world has a water shortage?
Impossible to say without more information. What is happening around the 2L for sale? Are you rejecting the sale based on price (i.e. preventing price from rising), instead selecting who gets it using some non-priced-based mechanism, such as a lottery or first-come, first-served? If yes, then that indicates that there is a shortage. If it is sold using a price-based mechanism, then clearly not. That is a "normally functioning" market.
Once the water is all used up and there is no remaining water supply, where no amount of money can buy more (i.e. preventing from rising), then perhaps you might say that there is a shortage. However, in the real world, absent of some other factor (e.g. price gouging laws), price will keep rising until you are compelled to make more of that water available, so that still wouldn't be a shortage situation.