i took eco101.. the term you are looking for is called consumer surplus:
"Consumer surplus is the economic gain accruing to a consumer (or consumers) when they engage in trade. The gain is the difference between the price they are willing to pay (or reservation price) and the actual price. If someone is willing to pay more than the actual price, their benefit in a transaction is how much they saved when they didn't pay that price"
the consumer surplus is normally very high on water but evaporates (heh) the second you go to a concert:)
Slashdot Mirror
the consumer surplus is normally very high on water but evaporates (heh) the second you go to a concert