Complex sentence: Pipes of a total length of greater than 13,000 miles are under the city's streets and pumping stations, testing and access stations provide for a relatively consistent and uniform supply of water which is highly regulated by water regulations.
Split into simpler sentences: Pipes of a total length of greater than are under the city's streets. These are supported by pumping, testing and access stations and together provide for a relatively consistent and uniform supply of water which is highly regulated by water regulations.