system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5 Imagine how much money and resource is spend shipping water around the world just part of everyday products. Why can we buy products then add the water at home?
gpt
Many things containing water cannot be isolated from the water and have their desired properties simply by reconstitution. These could be complex solutions involving chemicals "dissolved" in oil plus chemicals "dissolved" in alcohol and the parts dissolved in water. Food products, for example, are a complex mixture of the above.

Another method would be concentration and dilution. But this is also very problematic because many things are simply too dangerous when concentrated. A dilute acid cleaning product cannot simply be concentrated and sold, for example. Highly concentrated acid is too dangerous to handle.

In general, technology and businesses are not silly. They recognize the issues involved and would definitely want to save costs. Examples are that most sodas are bottled locally - the local manufacturers buy a syrup, dilute and pack it locally to reduce costs. 

If you want to know more, you have to be more specific. What particular "water" products are you thinking of?