A municipal water system end to end

From catchment to tap and back again. Every stage has its own regulator, its own failure modes and its own cost.

Indirect reuse: Treated effluent discharged upstream is abstracted again downstream. On heavily used rivers the same water may be used several times before reaching the sea.
Different regulators: In England, drinking water quality is the DWI, the environment is the Environment Agency, and economics is Ofwat. A failure can be one, two or all three of their concerns.
Where the cost is: Treatment is a minority of the cost. Most of it is in the pipes: laying, maintaining, repairing and eventually replacing hundreds of thousands of kilometres of network.

Text description

Rain falls on a catchment. Water is abstracted from a reservoir, river or borehole under licence, treated at a water treatment works, stored in service reservoirs, and distributed through a network of mains to properties. After use it enters the foul sewer, is treated at a wastewater treatment works, and is discharged back to a river, where it may be abstracted again downstream.