There is a big difference between bandwidth and water. After being built (which I grant can be substantial), the bulk of the costs to the water provider is the volume of water provided. If my neighbor uses twice the water I am, he's costing twice the same and should be charged the same.
But not all bytes are equal. If I am pulling 1 Linux DVD at 3am and my neighbor is pulling down 2 per night at 3am, the costs he is placing on the system are not twice mine. The actual electricity costs between moving his bits and my bits are negligible.
Instead, the cost is in building out the pipe to handle the maximum load each evening when everyone is pulling videos down and/or Skyping to Grandma. And even then not all bytes are equal. I might really want the voice packets of my Skype session to go through right now, but be able to tolerate several second of lag on the video I'm watching from Netflix, while letting the video of my Skype call degrade as needed.
I don't think you can put ISP regulations into one simple sentence. They need a more complicated and thus expensive regulatory regime. And, yes, the more complicated, the more subject it will be to lobbying pressure from people with different views from you. It still strikes me as the least-bad solution.
EDIT: Water and electricity providers do care about peak usage somewhat. Water companies need to keep up pressure, and electric companies need to keep the electrons flowing no matter what. But the water company can tolerate a 5% dip in water pressure, and electric companies have ways of, say, disabling AC units to juggle demand during especially high periods of usage.
I think we need some way of discouraging the single biggest consumers of the shared resource (such as charging them more) during peak usage while still providing incentive for the ISP to increase capacity. Lots of people fear that the ISPs would just use this to increase revenue instead of to properly ration a shared resource. I totally understand that fear because I trust my ISPs about as far I can throw their headquarters. But other providers of shared resources with much more predictable demand patterns still have ways of dealing with demand surges, so I don't see how ISPs could hope to function in the long-term without some kind of peak-demand management.