Note: Do not rely on this information. It is very old.
Value, and its economic sense, is the relation in which any one object of wealth stands to all others in regard to the amount of each which must be given when they are exchanged. All desirable things have a "value in use," but they do not require "value in exchange" unless there is some difficulty in obtaining them. Thus it is only under exceptional circumstances that water is valuable in the economic sense. Money being the medium of exchange, the price of a commodity is the index of its value, allowance being made for the fluctuation of the market.