Phil Stride, Head of the Thames Tideway Tunnel at Thames Water, says the company may not stand to make any profit from the project.
Thames Water has offered the following response to the claims from Hammersmith and Fulham Council:
Hammersmith and Fulham Council has accused Thames Water of ripping off its customers.
They claim that the super sewer isn't necessary - and that the company is being motivated by financial gain, rather than the environment.
The council argues that there are alternative solutions to the capital's sewage overflow problems - new drainage systems, for example, that could minimise the amount of fresh rain water entering the sewerage system.
They also claim that Thames Water stands to make "colossal returns at bill payers' expense".
Watch Thames Water's video below to find out about the construction of the super sewer.
THE CURRENT SITUATION
At the moment, our sewers fill up when it rains - and untreated waste water spills out into the River Thames.
THE PROPOSED SOLUTION
The new "super sewer" would divert the waste water away from the river.
When it rains in London, our old Victorian sewers fill up.
If the excess water isn't discharged somewhere, the sewage could back up into homes and streets. So, instead, it's released into the River Thames through "combined sewer overflows".
Thames Water says that, in a typical year, 39 million tonnes of untreated sewage flushes into the river. And - as the population of London increases - this problem is set to get worse.
So, they want to build a massive new sewer to increase the capacity of the system - and help clean up the River Thames.
Watch Thames Water's video below for more information.
The Thames Tideway Tunnel will be a new "super sewer", the width of three London buses, which will run underground from west to east London.
It will be around 20 miles long - and will broadly follow the route of the River Thames, connecting up to 34 sewer overflows.
Sewage, which would otherwise spill into the River Thames, will then be captured in the new tunnel and transferred to a waste water plant in Beckton to be treated.
Thames Water has released the following statement regarding the planned increase in water bills: