Building codes most likely mandate you either are on city sewer or have an approved septic system. They set it up so you cant evade it.
So if you have a private well and septic they can tax both. Because both have to be approved and regulated sothey then can tax them.
Ronald Reagan Quote: Government’s view of the economy could be summed up in a few short phrases: If it moves, tax it. If it keeps moving, regulate it. And if it stops moving, subsidize it.