Thames Water has announced that bills could go up by as much as £80 a year to help pay for a major new sewer.
Leaflets are being distributed to customers to warn them that they'll be charged more from 2014, in order to raise money for the Thames Tideway Tunnel.
The water company says that the super sewer is needed to help clean up the River Thames, as tens of millions of tonnes of untreated sewage currently overflow from London's Victorian sewers every year.
Water bills will have to go up, the leaflet warns, to help raise the £4.1 billion it will cost to complete the project.
But the project isn't without controversy. Hammersmith and Fulham Council has accused the company of acting for its own financial gain, rather than for the environment.
It claims 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) and that Thames Water stands to make "colossal returns at bill payers' expense".
The company refutes that allegation - saying that the project will not necessarily be carried out by Thames Water. If that's the case, the company will not make any profit whatsoever from the project.
Phil Stride from Thames Water goes into more detail on that point in the video clip below.
Our reporter Simon Harris sums up the arguments for and against the scheme in the video below.
WHAT IS THE THAMES TIDEWAY TUNNEL?
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.
WHY DOES SEWAGE CURRENTLY POUR INTO THE THAMES?
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".
The new sewer will increase the capacity of the system, so waste water no longer spills into the river.
Watch Thames Water's video below for more information.