Addis Ababa, in Ethiopia, is committing to cleaning up two of the riversides that flow through the city. That might be good, that might be bad – it depends upon how much is to be spent on cleaning up how much. There is actually an optimal level of pollution, or the inverse cleanliness, for a level of economic development. However, there is the one and only correct manner of collecting the benefits of this being done, through land value taxation:

Great, excellent. It really is possible to be too clean though – pollution becomes progressively more expensive to clean up and we can indeed get to the point where leaving some of the dirt while spending on other more urgent matters makes more sense.

But how should the city earn back what is spent?

The answer is tax that increased real estate value. This is how Hong Kong makes much of its government revenue. It’s how it pays for its metro system too – land values rise around a metro station, so, when building a new metro station pay for it by taxing those rising land values. This is also how the Battersea Tube extension in London is being paid for.

Economics is a general subject, we reach universal answers with it. Thus the answers in those rich world places, HK and London, are the same in a poor world one like Addis Ababa. Tax the rise in real estate values to pay for what it is that raises the real estate values.