A free good is a good with generally zero opportunity cost. This means that it can be consumed in much quantity as is required without reducing its availability to other consumers. A free good contrasts with an economic good which does have a value, an economic good has an opportunity cost. Free goods like air, water, intellectual ideas are all free goods that do not charge any price. They do not have an economic value till they are not scarce. Once the consumers face scarcity of water they will start charging for water.