induce you to reduce it by a second litre? By a third litre? To only one litre
consumed per week? The answer to the last question is quite a lot. The
fewer litres you are already using, the higher the marginal utility of one
additional litre of water.
1 Technically, incremental utility is measured over a discrete interval, such as from four juices to
five juices, whereas marginal utility is a rate of change measured over an infinitesimal interval.
However, common usage applies the word marginal when the last unit is involved, even if a one-
unit change is not infinitesimal. [9]