There was a time when computers ran on water.

No, really. They did. Check out the video above, a recent demonstration of a machine called the MONIAC, originally built in 1949. The MONIAC—short for Monetary National Income Analogue Computer—was a machine that analyzed economic data using, yes, hydraulics. Basically, it pumped water through pipes and tanks in an effort to simulate an economy and make predictions about its future.

The seven-foot-tall Rube Goldberg contraption may seem like a strange way to handle economic calculations, especially given that—ahem—drier computers of day could handle similar tasks. But as computer historian Doron Swade explains in an article for Inc., Phillips wanted a way to visualize the economy, and in those days, computers didn't have monitors.

Only about 14 MONIACs were made. Most of them are corroding in university basements around the world, but there are at least two working order, one at the Reserve Bank Museum in New Zealand and another at the University of Cambridge. The video above is an excerpt from a MONIAC demonstration by Cambridge engineering professor Allan McRobie, who restored the university's machine a few years ago.

The machine's various tanks and flows represent different parts of an economy, such as banks, consumer spending, personal savings, taxes, foreign holdings, and more. As McRobie explains, if you find that the personal savings tank is getting too full and you want to encourage more investment, you can simulate a drop in interest rates by widening the bank's valve so that money flows more freely through the system.

A more extensive demonstration is available on the Cambridge website. And you can see a software simulation of the machine's simulations on YouTube. But it's not as fun without real water.