I bet they won't have to pay it.
It's the same type of thing as a minimum base rate you normally pay for electric or water service, at least around here forever, probably others.
Even if you're gone all month, if you're on a municipal water supply there is a minimum charge. Last residence I had connected to county water supply it was for 2000 gallons a month, if the rate changed the $ amount changed. Same for electricity, but I don't know what it is because I've never been that low. The only people I ever knew that ran into the minimum had electricity at barns or something seasonal that was turned off when they weren't used. You still pay a minimum. This seems to be more of the same.
If you're connected to the grid, you should have an obligation to pay your share of maintenance and upgrade cost whether you use it or not. You want it available just in case, you have to pay for it.
The rate may be debatable, I have no idea of what would be proper. The requirement is understandable.