The Money Cycle

March 5, 2023

by Stephen Stofka

This week’s letter is about money and a natural resource like water. The nature of money, its origin and history have long been a subject of lively debate. What similarities and differences does money have with water? Does an analogy help uncover some less apparent characteristics of money? I’ll start with the three purposes of money that every economics student learns: a medium of exchange, a store of value and a unit of account. Coincidentally, water has three phases, gas, solid and liquid, and in each of those phases has some of the characteristics of money. The quantity of money can expand. The volume of water in all its phases is fixed.

Ice stores the energy of water the way that money stores value. As freezing water locks together in a crystal lattice, it becomes its own container. Oddly enough, most ice exhibits a hexagonal form, an efficient material transformation in response to changes in temperature. Only 2.5% of the world’s water is freshwater and most of that is locked up in glaciers. Money’s store of value is contained within assets.

In Part 5, Chapter 3 of the Wealth of Nations, Adam Smith noted that people tend to hoard their capital, to lock it away from a government which has little respect for individual property – what he called a “rude state of society.” If merchants and manufacturers have confidence in a government, they are willing to lend it money because the debt of that government can be traded in the market as though it were money. It is an interest bearing money. He lamented the fact that too many governments borrowed money to finance war and taxed people to build infrastructure. He suggested that governments do the opposite – borrow as much idle capital as possible to enhance the productivity of a country and tax people to finance wars. There would be less war and more progress.

Like money, water vapor is a medium of exchange between sky and ocean, between sky and earth. It is in constant motion within the atmosphere because its density quickly changes in response to changes in heat. It carries the water from the ocean and drops it onto the land in a conveyer belt system called the hydrological cycle. When all the earth came together in one supercontinent called Pangea 250 million years ago, water vapor transported little moisture from the oceans to the interior of the vast continent and the land was mostly desert (Howgego, 2016). When businesses around the world closed their doors at the onset of the pandemic in March 2020, we became very aware that our society, not just our economy, depends on a cycle of exchange.

Money is a unit of account, a common denominator to add up all the various goods and services in an economy. We add up tons of wheat and corn and millions of hours of labor in terms of money. . While we often think of fractions as “this divided by that,” economists understand fractions as “this in relation to that.” A social scientist might question whether it is a good idea for people to think of their labor in relation to money, the common denominator. Sadly, our society judges our worth to society in relation to that common denominator, money.

Water has a density like money has a purchasing power. Water is at its most dense – its weight per unit of volume – at 39°F and that benchmark is standardized at 1 in the metric system. The density of water at 39°F is like the benchmark price that economists use when they compute real GDP. Its volume expands as it gets colder or hotter than that temperature, so it’s density declines. The most measurable changes come at higher temperatures; at 200°F, the density is .963. We often use the language of heat when talking about inflation. The economy is overheating, for example. When there is hyperinflation¸ society itself begins to change state, just as water does at the boiling point.

Changes in the market value of our assets can have a material effect on our sense of safety. We work hard and save only a small portion of what we earn. When the value of an asset declines, it seems to melt away as though it were a block of ice on a sunny day. We may get a sense of helplessness or anxiety similar to the feeling we have when we lose electricity and worry that we will have to replace all the food in our fridge.

Readers may have other insights into money based on this water analogy. Just as equations can expose relationships that we did not understand before, analogies can do the same.


Photo by Ryan Yao on Unsplash

Howgego, J. (2016, July 14). Travel back in time to the most extreme desert and monsoons ever. New Scientist. Retrieved March 3, 2023, from

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