I wasn't actually arguing for water privatization, but rather I was arguing against blaming the free market for the current situation, one where the government owns most bodies of water and allowed this pollution.

I'm no expert on water privatization. I know a few economists have written about it, but it's unrealistic to expect them to come up with a great solution on their own. A good solution would have to evolve over time with decisions by judges etc.

AFAIK most proposals don't have a single entity owning a river, but rather people own rights to a certain amount of water from the river at a certain quality.

I wasn't referring to Walter Block's book on roads, but this one: "Water Capitalism: The Case for Privatizing Oceans, Rivers, Lakes, and Aquifers." I haven't read it.