Green Technology

Rentricity uses energy recovery techniques to get energy from " ...  excess pressure in water mains ..." and can generate " ... between 20 and 300 kilowatts of electricity..." 

Somewhat similar to wave energy but not really renewable.

The power can be sent to the grid and used to offset electricity purchases.

Since this electricity can then be sold onto the grid, Rentricity gives its generating partners an additional source of revenue and a way to offset rising electricity rates.

" ... no environmental impact and represent a new class of clean, renewable hydrokinetic energy. ... will produce hundreds of megawatts in aggregate."

 LINK to see diagram of system.

Via:  Rentricity  LINK