Why does Sydney pump sewage into the ocean and put its famous beaches at risk of poo balls?

Sydney Water plans to spend about $32bn to improve the sewerage system over the next 15 years in an attempt to reduce the amount of sewage sent to the coastal plants. Composite: Professor Jon Beves/AAP

In the first half of the 1900s, the mantra “the solution to pollution is dilution” ruled. The idea was that harmful chemicals and pollutants could be dealt with by spreading them out in the environment.

Now, that approach is derided as outdated and, often, dangerous.